design: document the multiport lane design

Describe what a lane is, the grouped socket layout, negotiation and port
pairing, how a lane comes up, how a flow stays on one lane and one routine
(including the kernel tun queue feedback loop that forces the lane to come
from the flow hash rather than the routine index), and every level at which
multiport falls back to the old single-port behavior.

.github/actions/code-sign/action.yml

@@ -25,9 +25,9 @@ inputs:
     required: false
     default: "code-signer"
   key-prefix:
-    description: "S3 key prefix the caller is authorized to write under"
+    description: "S3 key prefix to write under; defaults to code-signing/<owner>/<repo> of the calling repo"
     required: false
-    default: "code-signing/slackhq/nebula"
+    default: ""
 
 runs:
   using: composite
@@ -43,8 +43,15 @@ runs:
       with:
         role-to-assume: ${{ inputs.role }}
         aws-region: ${{ inputs.region }}
-        # Default is 12 retries to ride out IAM trust-policy propagation; once
-        # the role is stable we want a real misconfiguration to fail fast.
+        # An STS secret key with special characters does not survive the
+        # pwsh -> make -> MSYS sh -> aws.exe chain, and SigV4 then signs with a
+        # key that no longer matches, so the first S3 upload fails with
+        # SignatureDoesNotMatch. Retries the assume until it comes back clean.
+        # Same fix as DefinedNet/dnclient#867.
+        special-characters-workaround: true
+        # Overridden by the workaround above and kept for whenever that goes:
+        # the default 12 rides out IAM trust-policy propagation, and once the
+        # role is stable a real misconfiguration should fail fast.
         retry-max-attempts: 5
 
     - name: Sign .exe files
@@ -57,6 +64,9 @@ runs:
         KEY_PREFIX: ${{ inputs.key-prefix }}
       run: |
         set -eu
+        # Default the prefix to this repo so the S3 key attributes the sign correctly.
+        # nebula-nightly runs this same action but writes under its own repo's prefix.
+        KEY_PREFIX="${KEY_PREFIX:-code-signing/$GITHUB_REPOSITORY}"
         RUN="${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT}"
 
         find "$SIGN_PATH" -name '*.exe' -print | while read -r path

.github/workflows/release.yml

@@ -12,9 +12,9 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - uses: actions/setup-go@v6
+      - uses: actions/setup-go@v7
         with:
-          go-version: '1.25'
+          go-version: '1.26'
           check-latest: true
 
       - name: Build
@@ -38,9 +38,9 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - uses: actions/setup-go@v6
+      - uses: actions/setup-go@v7
         with:
-          go-version: '1.25'
+          go-version: '1.26'
           check-latest: true
 
       - name: Build
@@ -73,27 +73,81 @@ jobs:
   build-darwin:
     name: Build Universal Darwin
     env:
-      HAS_SIGNING_CREDS: ${{ secrets.AC_USERNAME != '' }}
+      HAS_SIGNING_CREDS: ${{ secrets.APPLE_SIGNING_ROLE_ARN != '' }}
     runs-on: macos-latest
+    permissions:
+      id-token: write
+      contents: read
     steps:
       - uses: actions/checkout@v7
 
-      - uses: actions/setup-go@v6
+      - uses: actions/setup-go@v7
         with:
-          go-version: '1.25'
+          go-version: '1.26'
           check-latest: true
 
+      # GitHub holds ARNs, not credentials, and ARNs outlive a rotation
+      - name: Configure AWS credentials
+        if: env.HAS_SIGNING_CREDS == 'true'
+        uses: aws-actions/configure-aws-credentials@v6
+        with:
+          role-to-assume: ${{ secrets.APPLE_SIGNING_ROLE_ARN }}
+          aws-region: us-east-2
+
+      # parse-json-secrets unpacks into SIGNING_* and ASC_*, masked on the way in
+      - name: Fetch signing credentials
+        if: env.HAS_SIGNING_CREDS == 'true'
+        uses: aws-actions/aws-secretsmanager-get-secrets@v3
+        with:
+          parse-json-secrets: true
+          secret-ids: |
+            SIGNING,${{ secrets.APPLE_SIGNING_DEVELOPER_ID_ARN }}
+            ASC,${{ secrets.APPLE_NOTARY_KEY_ARN }}
+
       - name: Import certificates
         if: env.HAS_SIGNING_CREDS == 'true'
         uses: Apple-Actions/import-codesign-certs@v7
         with:
-          p12-file-base64: ${{ secrets.APPLE_DEVELOPER_CERTIFICATE_P12_BASE64 }}
-          p12-password: ${{ secrets.APPLE_DEVELOPER_CERTIFICATE_PASSWORD }}
+          p12-file-base64: ${{ env.SIGNING_P12_BASE64 }}
+          p12-password: ${{ env.SIGNING_PASSWORD }}
+
+      # The action imports but does not check the chain validates, which is how a p12
+      # missing its intermediate reaches a failing codesign
+      - name: Check the identity is usable
+        if: env.HAS_SIGNING_CREDS == 'true'
+        run: |
+          : "${SIGNING_IDENTITY_SHA1:?empty, so the secret has no identity_sha1}"
+          identities=$(security find-identity -v -p codesigning signing_temp.keychain)
+          case "$identities" in
+          *"$SIGNING_IDENTITY_SHA1"*) ;;
+          *) printf '%s\n' "$identities" >&2; exit 1 ;;
+          esac
+
+      # notarytool wants the key as a file
+      - name: Write the App Store Connect key
+        if: env.HAS_SIGNING_CREDS == 'true'
+        run: |
+          mkdir -p ~/private_keys
+          chmod 700 ~/private_keys
+          key_path="$HOME/private_keys/AuthKey_${ASC_KEY_ID}.p8"
+          (umask 077; printf '%s\n' "$ASC_PRIVATE_KEY" > "$key_path")
+          echo "ASC_P8=$key_path" >> "$GITHUB_ENV"
+
+      - name: Drop the credentials from the environment
+        if: env.HAS_SIGNING_CREDS == 'true'
+        run: |
+          # The action's own inventory, so a new field in a secret is covered
+          python3 -c '
+          import json, os
+          raw = os.environ.get("SECRETS_LIST_CLEAN_UP")
+          if raw is None and os.environ.get("SIGNING_P12_BASE64"):
+              raise SystemExit("SECRETS_LIST_CLEAN_UP is gone, fetched secrets are not being scrubbed")
+          keep = {"SIGNING_IDENTITY_SHA1", "ASC_KEY_ID", "ASC_ISSUER_ID"}
+          names = [n for n in json.loads(raw or "[]") if n not in keep]
+          print("\n".join(f"{n}=" for n in dict.fromkeys(names)))
+          ' >> "$GITHUB_ENV"
 
       - name: Build, sign, and notarize
-        env:
-          AC_USERNAME: ${{ secrets.AC_USERNAME }}
-          AC_PASSWORD: ${{ secrets.AC_PASSWORD }}
         run: |
           rm -rf release
           mkdir release
@@ -102,17 +156,34 @@ jobs:
           lipo -create -output ./release/nebula ./build/darwin-amd64/nebula ./build/darwin-arm64/nebula
           lipo -create -output ./release/nebula-cert ./build/darwin-amd64/nebula-cert ./build/darwin-arm64/nebula-cert
 
-          if [ -n "$AC_USERNAME" ]; then
-            codesign -s "10BC1FDDEB6CE753550156C0669109FAC49E4D1E" -f -v --timestamp --options=runtime -i "net.defined.nebula" ./release/nebula
-            codesign -s "10BC1FDDEB6CE753550156C0669109FAC49E4D1E" -f -v --timestamp --options=runtime -i "net.defined.nebula-cert" ./release/nebula-cert
+          # Unset in a fork, which has no credentials to sign with
+          if [ -n "$SIGNING_IDENTITY_SHA1" ]; then
+            codesign -s "$SIGNING_IDENTITY_SHA1" -f -v --timestamp --options=runtime -i "net.defined.nebula" ./release/nebula
+            codesign -s "$SIGNING_IDENTITY_SHA1" -f -v --timestamp --options=runtime -i "net.defined.nebula-cert" ./release/nebula-cert
           fi
 
           zip -j release/nebula-darwin.zip release/nebula-cert release/nebula
 
-          if [ -n "$AC_USERNAME" ]; then
-            xcrun notarytool submit ./release/nebula-darwin.zip --team-id "576H3XS7FP" --apple-id "$AC_USERNAME" --password "$AC_PASSWORD" --wait
+          if [ -n "$ASC_P8" ]; then
+            xcrun notarytool submit ./release/nebula-darwin.zip --key "$ASC_P8" --key-id "$ASC_KEY_ID" --issuer "$ASC_ISSUER_ID" --wait
           fi
 
+      - name: Drop the signing key
+        if: always() && env.HAS_SIGNING_CREDS == 'true'
+        run: |
+          # Locked, not deleted: import-codesign-certs deletes it in its own post
+          # step and fails the job if it is already gone. Locked is unusable.
+          security lock-keychain signing_temp.keychain || true
+          rm -f "$ASC_P8"
+          # Nothing later in this job needs AWS
+          python3 -c '
+          import json, os
+          names = json.loads(os.environ.get("SECRETS_LIST_CLEAN_UP") or "[]")
+          names += ["ASC_P8", "SIGNING_IDENTITY_SHA1", "ASC_KEY_ID", "ASC_ISSUER_ID",
+                    "AWS_ACCESS_KEY_ID", "AWS_SECRET_ACCESS_KEY", "AWS_SESSION_TOKEN"]
+          print("\n".join(f"{n}=" for n in dict.fromkeys(names)))
+          ' >> "$GITHUB_ENV"
+
       - name: Upload artifacts
         uses: actions/upload-artifact@v7
         with:

.github/workflows/smoke-extra.yml

@@ -32,9 +32,9 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
         check-latest: true
 
     - name: add hashicorp source
@@ -64,9 +64,9 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
         check-latest: true
 
     - name: add hashicorp source
@@ -90,9 +90,9 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
         check-latest: true
 
     # WSL2 + Ubuntu so the smoke can run a real linux peer with its own

.github/workflows/smoke.yml

@@ -20,44 +20,45 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
+        check-latest: true
+
+    - name: Smoke Docker
+      run: make smoke-docker
+
+    - name: Smoke Docker IPv6 overlay
+      run: make smoke-docker-ipv6
+
+    - name: Smoke Relay Docker
+      run: make smoke-relay-docker
+
+    - name: Smoke Docker boringcrypto
+      run: make boringcrypto smoke-docker
+
+    - name: Smoke Docker fips140
+      run: make fips140-all GOALS=smoke-docker
+
+    timeout-minutes: 10
+
+  smoke-self:
+    name: Run self traffic smoke test on macOS
+    runs-on: macos-latest
+    steps:
+
+    - uses: actions/checkout@v7
+
+    - uses: actions/setup-go@v7
+      with:
+        go-version: '1.26'
         check-latest: true
 
     - name: build
-      run: make bin-docker CGO_ENABLED=1 BUILD_ARGS=-race
+      run: make bin
 
-    - name: setup docker image
+    - name: run smoke-self
       working-directory: ./.github/workflows/smoke
-      run: ./build.sh
-
-    - name: run smoke
-      working-directory: ./.github/workflows/smoke
-      run: ./smoke.sh
-
-    - name: setup docker image ipv6
-      working-directory: ./.github/workflows/smoke
-      run: SMOKE_OVERLAY_IPV6=1 ./build.sh
-
-    - name: run smoke ipv6
-      working-directory: ./.github/workflows/smoke
-      run: SMOKE_OVERLAY_IPV6=1 ./smoke.sh
-
-    - name: setup relay docker image
-      working-directory: ./.github/workflows/smoke
-      run: ./build-relay.sh
-
-    - name: run smoke relay
-      working-directory: ./.github/workflows/smoke
-      run: ./smoke-relay.sh
-
-    - name: setup docker image for P256
-      working-directory: ./.github/workflows/smoke
-      run: NAME="smoke-p256" CURVE=P256 ./build.sh
-
-    - name: run smoke-p256
-      working-directory: ./.github/workflows/smoke
-      run: NAME="smoke-p256" ./smoke.sh
+      run: ./smoke-self.sh
 
     timeout-minutes: 10

.github/workflows/smoke/smoke-self.sh

@@ -0,0 +1,130 @@
+#!/bin/bash
+
+# A host must be able to reach its own overlay address. Where the kernel sends
+# that traffic through the tun rather than over loopback, nebula sees it and
+# hands it straight back (immediatelyForwardToSelf), and whether the kernel
+# accepts what comes back is only answerable against a real kernel. Runs one
+# nebula on this machine as root and aims every probe at its own address.
+
+set -e -x
+
+set -o pipefail
+
+V4=192.0.2.1
+V6=2001:db8::1
+
+case "$(uname -s)" in
+    Darwin) TUN_DEV=utun ;;
+    *) TUN_DEV=tun0 ;;
+esac
+
+ROOT="$(cd ../../.. && pwd)"
+
+rm -rf build/self
+mkdir -p build/self
+cd build/self
+
+cleanup() {
+    echo
+    echo " *** cleanup"
+    echo
+
+    set +e
+    if [ -n "$NEBULA_PID" ]
+    then
+        sudo kill "$NEBULA_PID"
+    fi
+    { kill $(jobs -p); wait; } 2>/dev/null
+    sed 's/^/  [self]  /' nebula.log
+}
+
+trap cleanup EXIT
+
+# perl is on every platform this runs on; timeout(1) is not.
+alarm() {
+    perl -e 'alarm shift; exec @ARGV' "$@"
+}
+
+RESULTS=""
+FAILED=""
+probe() {
+    local name="$1"
+    shift
+    if "$@"
+    then
+        RESULTS="$RESULTS $name=ok"
+    else
+        RESULTS="$RESULTS $name=FAIL"
+        FAILED="$FAILED $name"
+    fi
+}
+
+# Send one datagram, then wait for the listener to have written it out.
+udp_probe() {
+    echo self | alarm 5 nc -u -w1 "$1" 3000 || true
+    set +x
+    for _ in $(seq 1 20)
+    do
+        if grep -q self "$2"
+        then
+            set -x
+            return 0
+        fi
+        sleep 0.25
+    done
+    set -x
+    return 1
+}
+
+"$ROOT/nebula-cert" ca -name "Smoke Test"
+"$ROOT/nebula-cert" sign -name self -networks "$V4/24,$V6/64"
+
+HOST=self AM_LIGHTHOUSE=true TUN_DEV="$TUN_DEV" ../../genconfig.sh >self.yml
+
+"$ROOT/nebula" -config self.yml -test
+
+sudo -v
+sudo "$ROOT/nebula" -config self.yml >nebula.log 2>&1 &
+NEBULA_PID=$!
+
+for _ in $(seq 1 40)
+do
+    ifconfig | grep "inet6 $V6 " >/dev/null && break
+    sleep 0.25
+done
+ifconfig | grep "inet $V4 "
+ifconfig | grep "inet6 $V6 "
+
+nc -l "$V4" 2000 >/dev/null &
+nc -l "$V6" 2000 >/dev/null &
+nc -u -l "$V4" 3000 >udp4.txt &
+nc -u -l "$V6" 3000 >udp6.txt &
+sleep 1
+
+set +x
+echo
+echo " *** Testing self traffic from $V4"
+echo
+set -x
+probe icmp4 alarm 5 ping -c1 "$V4"
+probe tcp4 alarm 5 nc -z "$V4" 2000
+probe udp4 udp_probe "$V4" udp4.txt
+
+set +x
+echo
+echo " *** Testing self traffic from $V6"
+echo
+set -x
+probe icmp6 alarm 5 ping6 -c1 "$V6"
+probe tcp6 alarm 5 nc -z "$V6" 2000
+probe udp6 udp_probe "$V6" udp6.txt
+
+set +x
+echo
+echo " *** self traffic:$RESULTS"
+echo
+if [ -n "$FAILED" ]
+then
+    echo "self traffic failed:$FAILED" >&2
+    exit 1
+fi

.github/workflows/test.yml

@@ -20,9 +20,9 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
         check-latest: true
 
     - name: Install goimports
@@ -42,7 +42,7 @@ jobs:
     - name: golangci-lint
       uses: golangci/golangci-lint-action@v9
       with:
-        version: v2.5
+        version: v2.12
 
   test:
     name: Test ${{ matrix.name }}
@@ -58,9 +58,14 @@ jobs:
           e2e-cmd: make e2evv
         - name: linux-boringcrypto
           os: ubuntu-latest
-          build-cmd: make bin-boringcrypto
-          test-cmd: make test-boringcrypto
-          e2e-cmd: make e2e GOEXPERIMENT=boringcrypto CGO_ENABLED=1 TEST_ENV="TEST_LOGS=1" TEST_FLAGS="-v -ldflags -checklinkname=0"
+          build-cmd: make boringcrypto
+          test-cmd: make boringcrypto test
+          e2e-cmd: make boringcrypto e2evv
+        - name: linux-fips140
+          os: ubuntu-latest
+          build-cmd: make fips140-all
+          test-cmd: make fips140-all GOALS=test
+          e2e-cmd: make fips140-all GOALS=e2evv
         - name: linux-pkcs11
           os: ubuntu-latest
           build-cmd: make bin-pkcs11
@@ -80,9 +85,9 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
         check-latest: true
 
     - name: Build
@@ -125,9 +130,9 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - uses: actions/setup-go@v6
+    - uses: actions/setup-go@v7
       with:
-        go-version: '1.25'
+        go-version: '1.26'
         check-latest: true
 
     - name: Build ${{ matrix.name }}

CHANGELOG.md

@@ -7,6 +7,102 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- IPv6 packets whose next header is a protocol Nebula does not parse (SCTP, GRE, IP-in-IP, etc.) are now
+  classified as that protocol with no ports, closing a firewall bypass where a crafted payload could steer
+  the classifier into reading one as TCP/UDP and matching a TCP/UDP rule. These packets are now matched as
+  their true protocol, so only a `proto: any` rule allows them. If you carry one of these protocols over the
+  overlay, confirm a `proto: any` rule covers it before upgrading, it may have been passing only through this
+  bypass. (#1840)
+
+### Fixed
+
+- The ICMPv6 type was read from the wrong byte when classifying IPv6 packets, so the echo identifier used
+  for conntrack was never picked up. (#1840)
+
+## [1.11.0] - 2026-07-23
+
+See the [v1.11.0](https://github.com/slackhq/nebula/milestone/25?closed=1) milestone for a complete list of changes.
+
+### Breaking
+
+- Logging has switched from logrus to Go's structured `slog`. Log output changes: levels are upper case
+  (`level=INFO`), trace prints as `level=DEBUG-4`, timestamps are always RFC3339Nano and `logging.timestamp_format`
+  is ignored, and some messages were reworded. Review any log parsing before upgrading. This is also an API break
+  for embedders, as constructors now take a `*slog.Logger`. (#1672, #1734, #1621)
+- `firewall.inbound_action` and `firewall.outbound_action` (used to set reject vs. drop policy) were each being
+  applied to the opposite direction, that is now corrected. This only affects how blocked packets are answered, not
+  which packets the firewall allows or denies. If you set either of these you are getting the behavior of the other
+  one today and likely want to swap them before upgrading. (#1798)
+- On Windows, Nebula now installs WFP PERMIT filters for the nebula adapter and the listener port by default. WFP
+  sits below Windows Defender Firewall, so any WDF inbound rules you rely on for either will no longer apply. Set
+  `tun.windows_bypass_wdf` and `listen.windows_bypass_wdf` to false to leave WDF in charge. (#1710)
+- On Windows, the nebula device is now set to the `private` network category instead of whatever Windows decided,
+  which is usually `Public`. This makes the host firewall less restrictive on the overlay. Set
+  `tun.network_category` to `unset` to keep the old behavior. (#1710)
+- Reject packets for non-TCP now use ICMP code 13, communication administratively prohibited, instead of code 3,
+  port unreachable. Anything keying off the old code needs updating. (#1766, #1768)
+- The SSH debug server's profiling commands are now confined to `sshd.sandbox_dir`, which defaults to
+  `$TMP/nebula-debug`. Relative paths resolve inside it and absolute paths outside it are rejected, so anything
+  scripting `start-cpu-profile`, `save-heap-profile`, or `save-mutex-profile` with a path elsewhere needs the
+  directory set. The directory is not created for you. (#1622)
+
+### Added
+
+- Sign the Windows release binaries. (#1718)
+- Generate IPv6 reject packets, matching the existing IPv4 behavior. (#1766, #1767, #1768)
+- Accept `-` in `nebula-cert` to read from stdin or write to stdout. (#1714)
+- Search for both `config.yml` and `config.yaml` in service and command line modes. (#1717)
+- Add version labels to the Docker/OCI images. (#1772)
+- Rebind the listener and re-query lighthouses on macOS when the underlay network changes, so devices moving
+  between wifi and wired or between networks recover without waiting for dead tunnel detection. Controlled by
+  `listen.rebind_on_network_change` (default `true`, not reloadable). (#1816)
+
+### Changed
+
+- Reload the firewall when the unsafe networks in the certificate change. (#1719)
+- Reconfigure, start, and stop the stats listener on a config reload instead of requiring a restart. (#1670)
+- Update a static host's addresses when they change on reload. (#1713)
+- Don't require a port on ICMP firewall rules. (#1609)
+- Connection track ICMP traffic. (#1602)
+- Return `NODATA` instead of `NXDOMAIN` from the DNS server for a name that exists but has no record of the
+  requested type, so clients that query `AAAA` first (busybox/Alpine) fall through to `A`. (#1668)
+- Record the local host's details in the DNS server. (#1716)
+- Install Windows unsafe routes as link routes. (#1709)
+- Reduce relay handshake log spam, and only log a handshake send error at error level when the remote list
+  changes. (#1733, #1765, #1810)
+- Start, stop, and reload subsystems (DNS, stats, conntrack, ssh, punchy) cleanly without leaking goroutines. (#1640, #1654, #1661, #1667, #1669, #1708, #1806, #1815)
+- `Control` is now safe to stop and wait on from any lifecycle state, and a new `Control.Wait` blocks until nebula
+  has fully stopped and returns the first fatal reader error. Failed starts release the udp sockets and tun fd
+  instead of leaking them. (#1794)
+- Trigger an immediate lighthouse update when reconnecting to or adding a lighthouse instead of waiting for the next update tick. (#1645)
+- Bring the Darwin and OpenBSD tun implementations in line with the other BSDs. (#1703)
+- Update to build against go v1.26. (#1818)
+- Various dependency updates. (#1586, #1587, #1604, #1617, #1618, #1627, #1628, #1629, #1652, #1664, #1665, #1697, #1721, #1732, #1742, #1743, #1750, #1763, #1771, #1782, #1800, #1807)
+
+### Fixed
+
+- Fix a data race on a host's remote address that could send packets to the wrong address during a roam. (#1773)
+- Fix tunnels that could permanently escape connection manager monitoring. (#1752)
+- Fix a crash when reloading the SSH server's trusted keys. (#1787)
+- Fix hostmap corruption when a host has multiple overlay addresses. Each address now gets its own list instead of
+  a single shared chain, which also fixes two latent bugs on the add and makePrimary paths. (#1788, #1790)
+- Apply `remote_allow_list` IPv4 rules to 4-in-6 mapped addresses. (#1786)
+- Don't panic in the DNS server on a short or empty query name. (#1635)
+- Advance the replay window on relayed packets so a relay drops replayed frames instead of re-forwarding them. (#1751)
+- Fix a race in relay state handling. (#1753)
+- Lock replay window updates so concurrent readers can't corrupt it. (#1802)
+- Reject malformed handshakes more reliably, including invalid ed25519 key lengths. (#1601, #1756)
+- Properly handle `closetunnel` packets. (#1638)
+- Fix an IPv6 extension-header length overflow that could make the firewall parse the wrong protocol and ports. (#1789)
+- Fix relay re-establishment when a handshake arrives over a relay entry that a one-sided teardown left
+  `Disestablished`, which silently dropped every send until dead tunnel detection forced a re-handshake. (#1805)
+- Don't build new relay state on a tunnel that was just discarded. (#1796)
+- Don't delete the wrong pending hostinfo in the handshake manager. (#1811)
+- Don't call the packet reader after a UDP error on Darwin. (#1755)
+- Open the FreeBSD tun device non blocking. (#1666)
+
 ## [1.10.3] - 2026-02-06
 
 ### Security

Makefile

@@ -72,6 +72,17 @@ ALL_CROSS_LINUX_ARM   = linux-arm-5 linux-arm-6 linux-arm-7 linux-arm64
 ALL_CROSS_LINUX_MIPS  = linux-mips linux-mipsle linux-mips64 linux-mips64le linux-mips-softfloat
 ALL_CROSS_LINUX_OTHER = linux-386 linux-ppc64le linux-riscv64 linux-loong64
 
+# Based on section 2.2 of the Go Cryptographic Module CVMP Security Policy #5247
+ALL_FIPS140 = linux-amd64-fips140 \
+	linux-arm64-fips140 \
+	windows-amd64-fips140 \
+	windows-arm64-fips140 \
+	darwin-arm64-fips140 \
+	freebsd-amd64-fips140 \
+	linux-arm-7-fips140 \
+	linux-mips64-fips140 \
+	linux-ppc64le-fips140
+
 e2e:
 	$(TEST_ENV) go test -tags=e2e_testing -count=1 $(TEST_FLAGS) ./e2e
 
@@ -137,6 +148,8 @@ release-netbsd: $(ALL_NETBSD:%=build/nebula-%.tar.gz)
 
 release-boringcrypto: build/nebula-linux-$(shell go env GOARCH)-boringcrypto.tar.gz
 
+release-fips140: $(ALL_FIPS140:%=build/nebula-%.tar.gz)
+
 BUILD_ARGS += -trimpath
 
 bin-windows: build/windows-amd64/nebula.exe build/windows-amd64/nebula-cert.exe
@@ -157,17 +170,24 @@ bin-freebsd-arm64: build/freebsd-arm64/nebula build/freebsd-arm64/nebula-cert
 bin-boringcrypto: build/linux-$(shell go env GOARCH)-boringcrypto/nebula build/linux-$(shell go env GOARCH)-boringcrypto/nebula-cert
 	mv $? .
 
+bin-fips140: build/linux-$(shell go env GOARCH)-fips140/nebula build/linux-$(shell go env GOARCH)-fips140/nebula-cert
+	mv $? .
+
 bin-pkcs11: BUILD_ARGS += -tags pkcs11
 bin-pkcs11: CGO_ENABLED = 1
 bin-pkcs11: bin
 
+# Build with the pprof debug server (serves on :6060). See startPprofServer.
+debug: BUILD_ARGS += -tags debug
+debug: bin
+
 bin:
-	go build $(BUILD_ARGS) -ldflags "$(LDFLAGS)" -o ./nebula${NEBULA_CMD_SUFFIX} ${NEBULA_CMD_PATH}
-	go build $(BUILD_ARGS) -ldflags "$(LDFLAGS)" -o ./nebula-cert${NEBULA_CMD_SUFFIX} ./cmd/nebula-cert
+	$(GOENV) go build $(BUILD_ARGS) -ldflags "$(LDFLAGS)" -o ./nebula${NEBULA_CMD_SUFFIX} ${NEBULA_CMD_PATH}
+	$(GOENV) go build $(BUILD_ARGS) -ldflags "$(LDFLAGS)" -o ./nebula-cert${NEBULA_CMD_SUFFIX} ./cmd/nebula-cert
 
 install:
-	go install $(BUILD_ARGS) -ldflags "$(LDFLAGS)" ${NEBULA_CMD_PATH}
-	go install $(BUILD_ARGS) -ldflags "$(LDFLAGS)" ./cmd/nebula-cert
+	$(GOENV) go install $(BUILD_ARGS) -ldflags "$(LDFLAGS)" ${NEBULA_CMD_PATH}
+	$(GOENV) go install $(BUILD_ARGS) -ldflags "$(LDFLAGS)" ./cmd/nebula-cert
 
 build/linux-arm-%: GOENV += GOARM=$(word 3, $(subst -, ,$*))
 build/linux-mips-%: GOENV += GOMIPS=$(word 3, $(subst -, ,$*))
@@ -178,8 +198,11 @@ build/linux-mips-softfloat/%: LDFLAGS += -s -w
 # boringcrypto
 build/linux-amd64-boringcrypto/%: GOENV += GOEXPERIMENT=boringcrypto CGO_ENABLED=1
 build/linux-arm64-boringcrypto/%: GOENV += GOEXPERIMENT=boringcrypto CGO_ENABLED=1
-build/linux-amd64-boringcrypto/%: LDFLAGS += -checklinkname=0
-build/linux-arm64-boringcrypto/%: LDFLAGS += -checklinkname=0
+
+# fips140
+FIPSVERSION = v1.0.0
+$(foreach _rule, $(ALL_FIPS140), build/$(_rule)/%): GOENV += GOFIPS140=$(FIPSVERSION)
+$(foreach _rule, $(ALL_FIPS140), build/$(_rule)/%): BUILD_ARGS += -tags fips140enforce
 
 build/%/nebula: .FORCE
 	GOOS=$(firstword $(subst -, , $*)) \
@@ -210,10 +233,7 @@ vet:
 	go vet $(VET_FLAGS) -v ./...
 
 test:
-	go test -v ./...
-
-test-boringcrypto:
-	GOEXPERIMENT=boringcrypto CGO_ENABLED=1 go test -ldflags "-checklinkname=0" -v ./...
+	$(TEST_ENV) go test $(TEST_FLAGS) -v ./...
 
 test-pkcs11:
 	CGO_ENABLED=1 go test -v -tags pkcs11 ./...
@@ -256,29 +276,75 @@ ifeq ($(words $(MAKECMDGOALS)),1)
 	@$(MAKE) service ${.DEFAULT_GOAL} --no-print-directory
 endif
 
+# Useful to chain together, like:
+# - make fips140 e2evv
+# - make fips140 smoke-docker
+# Use `release-fips140` to build release binaries
+fips140:
+	@echo > $(NULL_FILE)
+ifeq ($(strip $(GOFIPS140)),)
+	$(eval GOFIPS140 = $(FIPSVERSION))
+endif
+	$(eval GOENV += GOFIPS140=$(GOFIPS140))
+	$(eval BUILD_ARGS += -tags fips140enforce)
+	$(eval TEST_ENV += $(GOENV))
+	$(eval CURVE = P256)
+ifeq ($(words $(MAKECMDGOALS)),1)
+	@$(MAKE) fips140 GOFIPS140=$(GOFIPS140) ${.DEFAULT_GOAL} --no-print-directory
+endif
+
+# To test the future pending module, use like `make fips140-latest test`
+ALL_GOFIPS140 = v1.0.0 v1.26.0 latest
+define FIPS140_rule
+fips140-$(1): GOFIPS140 = $(1)
+fips140-$(1): fips140
+endef
+$(foreach _rule, $(ALL_GOFIPS140), $(eval $(call FIPS140_rule,$(_rule))))
+
+# Iterate and run the goals for all fips versions, like `make fips140-all GOALS=test`
+fips140-all:
+	@$(foreach _v,$(ALL_GOFIPS140),$(MAKE) fips140-$(_v) $(GOALS) &&) true
+
+# Useful to chain together, like:
+# - make boringcrypto e2evv
+# - make boringcrypto smoke-docker
+# Use `release-boringcrypto` or `bin-boringcrypto` to build release binaries
+boringcrypto:
+	@echo > $(NULL_FILE)
+	$(eval GOENV += GOEXPERIMENT=boringcrypto CGO_ENABLED=1)
+	$(eval TEST_ENV += $(GOENV))
+	$(eval CURVE = P256)
+ifeq ($(words $(MAKECMDGOALS)),1)
+	@$(MAKE) boringcrypto ${.DEFAULT_GOAL} --no-print-directory
+endif
+
 bin-docker: bin build/linux-amd64/nebula build/linux-amd64/nebula-cert
 
+smoke-docker: BUILD_ARGS += -race
+smoke-docker: GOENV += CGO_ENABLED=1
 smoke-docker: bin-docker
-	cd .github/workflows/smoke/ && ./build.sh
-	cd .github/workflows/smoke/ && ./smoke.sh
-	cd .github/workflows/smoke/ && NAME="smoke-p256" CURVE="P256" ./build.sh
-	cd .github/workflows/smoke/ && NAME="smoke-p256" ./smoke.sh
+	# This is so we can limit `fips140` smoke test to just P256 curve.
+	if [ "$(CURVE)" != "P256" ]; then cd .github/workflows/smoke/ && $(GOENV) ./build.sh; fi
+	if [ "$(CURVE)" != "P256" ]; then cd .github/workflows/smoke/ && $(GOENV) ./smoke.sh; fi
+	cd .github/workflows/smoke/ && $(GOENV) NAME="smoke-p256" CURVE="P256" ./build.sh
+	cd .github/workflows/smoke/ && $(GOENV) NAME="smoke-p256" ./smoke.sh
 
+smoke-relay-docker: BUILD_ARGS += -race
+smoke-relay-docker: GOENV += CGO_ENABLED=1
 smoke-relay-docker: bin-docker
-	cd .github/workflows/smoke/ && ./build-relay.sh
-	cd .github/workflows/smoke/ && ./smoke-relay.sh
+	cd .github/workflows/smoke/ && $(GOENV) ./build-relay.sh
+	cd .github/workflows/smoke/ && $(GOENV) ./smoke-relay.sh
 
 smoke-docker-ipv6: export SMOKE_OVERLAY_IPV6 = 1
 smoke-docker-ipv6: smoke-docker
 
-smoke-docker-race: BUILD_ARGS = -race
-smoke-docker-race: CGO_ENABLED = 1
-smoke-docker-race: smoke-docker
+smoke-self: bin
+	cd .github/workflows/smoke/ && ./smoke-self.sh
 
 smoke-vagrant/%: bin-docker build/%/nebula
 	cd .github/workflows/smoke/ && ./build.sh $*
 	cd .github/workflows/smoke/ && ./smoke-vagrant.sh $*
 
 .FORCE:
-.PHONY: all all-linux all-freebsd all-openbsd all-netbsd all-darwin all-windows all-cross-linux all-cross-linux-arm all-cross-linux-mips all-cross-linux-other all-cross-darwin all-cross-windows bench bench-cpu bench-cpu-long bin build-test-mobile e2e e2ev e2evv e2evvv e2evvvv proto release service smoke-docker smoke-docker-race test test-cov-html smoke-vagrant/%
+.PHONY: all all-linux all-freebsd all-openbsd all-netbsd all-darwin all-windows all-cross-linux all-cross-linux-arm all-cross-linux-mips all-cross-linux-other all-cross-darwin all-cross-windows bench bench-cpu bench-cpu-long bin bin-windows bin-windows-arm64 bin-darwin bin-freebsd bin-freebsd-arm64 bin-boringcrypto bin-fips140 bin-pkcs11 bin-docker boringcrypto build-test-mobile debug docker e2e e2ev e2evv e2evvv e2evvvv e2e-bench fips140 fips140-all $(ALL_GOFIPS140:%=fips140-%) install proto release release-linux release-freebsd release-openbsd release-netbsd release-boringcrypto release-fips140 service smoke-docker smoke-relay-docker smoke-docker-ipv6 smoke-self test test-pkcs11 test-cov-html vet smoke-vagrant/%
 .DEFAULT_GOAL := bin

README.md

@@ -145,17 +145,27 @@ To build nebula for a specific platform (ex, Windows):
 
 See the [Makefile](Makefile) for more details on build targets
 
-## Curve P256 and BoringCrypto
+## Curve P256 and FIPS 140-3 mode
 
 The default curve used for cryptographic handshakes and signatures is Curve25519. This is the recommended setting for most users. If your deployment has certain compliance requirements, you have the option of creating your CA using `nebula-cert ca -curve P256` to use NIST Curve P256. The CA will then sign certificates using ECDSA P256, and any hosts using these certificates will use P256 for ECDH handshakes.
 
-In addition, Nebula can be built using the [BoringCrypto GOEXPERIMENT](https://github.com/golang/go/blob/go1.20/src/crypto/internal/boring/README.md) by running either of the following make targets:
+Nebula can be built to support the [FIPS 140-3](https://go.dev/doc/security/fips140) mode of Go by running either of the following make targets. (This sets GOFIPS140=v1.0.0, which must be done at compile time so that the correct AES-GCM can be used for FIPS 140-3 enforcement mode).
+
+```sh
+make fips140
+make fips140 test
+make release-fips140
+```
+
+Nebula can also be built using the [BoringCrypto GOEXPERIMENT](https://github.com/golang/go/blob/go1.20/src/crypto/internal/boring/README.md) by running either of the following make targets.
 
 ```sh
 make bin-boringcrypto
 make release-boringcrypto
 ```
 
+NOTE: boringcrypto support is deprecated and will be removed in the next release. Users should migrate to the native FIPS 140-3 mode described above.
+
 This is not the recommended default deployment, but may be useful based on your compliance requirements.
 
 ## Credits

cmd/nebula-cert/ca.go

@@ -3,11 +3,14 @@ package main
 import (
 	"crypto/ecdsa"
 	"crypto/elliptic"
+	"crypto/fips140"
 	"crypto/rand"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
 	"math"
+	"math/bits"
 	"net/netip"
 	"os"
 	"strings"
@@ -43,7 +46,28 @@ type caFlags struct {
 	subnets *string
 }
 
+func defaultCurve() string {
+	if fips140.Enforced() {
+		return "P256"
+	}
+	return "25519"
+}
+
 func newCaFlags() *caFlags {
+	// prevent running out of memory on 32-bit systems by defaulting to
+	// RFC9106's recommendation for memory-constrained environments
+	var (
+		defaultArgonMemory     uint
+		defaultArgonIterations uint
+	)
+	if bits.UintSize == 32 {
+		defaultArgonMemory = 64 * 1024
+		defaultArgonIterations = 3
+	} else {
+		defaultArgonMemory = 2 * 1024 * 1024
+		defaultArgonIterations = 1
+	}
+
 	cf := caFlags{set: flag.NewFlagSet("ca", flag.ContinueOnError)}
 	cf.set.Usage = func() {}
 	cf.name = cf.set.String("name", "", "Required: name of the certificate authority")
@@ -55,11 +79,11 @@ func newCaFlags() *caFlags {
 	cf.groups = cf.set.String("groups", "", "Optional: comma separated list of groups. This will limit which groups subordinate certs can use")
 	cf.networks = cf.set.String("networks", "", "Optional: comma separated list of ip address and network in CIDR notation. This will limit which ip addresses and networks subordinate certs can use in networks")
 	cf.unsafeNetworks = cf.set.String("unsafe-networks", "", "Optional: comma separated list of ip address and network in CIDR notation. This will limit which ip addresses and networks subordinate certs can use in unsafe networks")
-	cf.argonMemory = cf.set.Uint("argon-memory", 2*1024*1024, "Optional: Argon2 memory parameter (in KiB) used for encrypted private key passphrase")
+	cf.argonMemory = cf.set.Uint("argon-memory", defaultArgonMemory, "Optional: Argon2 memory parameter (in KiB) used for encrypted private key passphrase")
 	cf.argonParallelism = cf.set.Uint("argon-parallelism", 4, "Optional: Argon2 parallelism parameter used for encrypted private key passphrase")
-	cf.argonIterations = cf.set.Uint("argon-iterations", 1, "Optional: Argon2 iterations parameter used for encrypted private key passphrase")
+	cf.argonIterations = cf.set.Uint("argon-iterations", defaultArgonIterations, "Optional: Argon2 iterations parameter used for encrypted private key passphrase")
 	cf.encryption = cf.set.Bool("encrypt", false, "Optional: prompt for passphrase and write out-key in an encrypted format")
-	cf.curve = cf.set.String("curve", "25519", "EdDSA/ECDSA Curve (25519, P256)")
+	cf.curve = cf.set.String("curve", defaultCurve(), "EdDSA/ECDSA Curve (25519, P256)")
 	cf.p11url = p11Flag(cf.set)
 
 	cf.ips = cf.set.String("ips", "", "Deprecated, see -networks")
@@ -244,6 +268,9 @@ func ca(args []string, out io.Writer, errOut io.Writer, pr PasswordReader) error
 	} else {
 		switch *cf.curve {
 		case "25519", "X25519", "Curve25519", "CURVE25519":
+			if fips140.Enforced() {
+				return errors.New("use of Curve25519 is not allowed in FIPS 140-only mode")
+			}
 			curve = cert.Curve_CURVE25519
 			pub, rawPriv, err = ed25519.GenerateKey(rand.Reader)
 			if err != nil {

cmd/nebula-cert/ca_test.go

@@ -7,7 +7,9 @@ import (
 	"bytes"
 	"encoding/pem"
 	"errors"
+	"math/bits"
 	"os"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -22,6 +24,18 @@ func Test_caSummary(t *testing.T) {
 }
 
 func Test_caHelp(t *testing.T) {
+	var (
+		defaultArgonMemory     string
+		defaultArgonIterations string
+	)
+	if bits.UintSize == 32 {
+		defaultArgonMemory = strconv.Itoa(64 * 1024)
+		defaultArgonIterations = strconv.Itoa(3)
+	} else {
+		defaultArgonMemory = strconv.Itoa(2 * 1024 * 1024)
+		defaultArgonIterations = strconv.Itoa(1)
+	}
+
 	ob := &bytes.Buffer{}
 	caHelp(ob)
 	assert.Equal(
@@ -29,9 +43,9 @@ func Test_caHelp(t *testing.T) {
 		"Usage of "+os.Args[0]+" ca <flags>: create a self signed certificate authority\n"+
 			"  Pass \"-\" to any path flag to read from stdin or write to stdout.\n"+
 			"  -argon-iterations uint\n"+
-			"    \tOptional: Argon2 iterations parameter used for encrypted private key passphrase (default 1)\n"+
+			"    \tOptional: Argon2 iterations parameter used for encrypted private key passphrase (default "+defaultArgonIterations+")\n"+
 			"  -argon-memory uint\n"+
-			"    \tOptional: Argon2 memory parameter (in KiB) used for encrypted private key passphrase (default 2097152)\n"+
+			"    \tOptional: Argon2 memory parameter (in KiB) used for encrypted private key passphrase (default "+defaultArgonMemory+")\n"+
 			"  -argon-parallelism uint\n"+
 			"    \tOptional: Argon2 parallelism parameter used for encrypted private key passphrase (default 4)\n"+
 			"  -curve string\n"+
@@ -188,10 +202,16 @@ func Test_ca(t *testing.T) {
 	k, _ := pem.Decode(rb)
 	ned, err := cert.UnmarshalNebulaEncryptedData(k.Bytes)
 	require.NoError(t, err)
-	// we won't know salt in advance, so just check start of string
-	assert.Equal(t, uint32(2*1024*1024), ned.EncryptionMetadata.Argon2Parameters.Memory)
+
+	if bits.UintSize == 32 {
+		assert.Equal(t, uint32(64*1024), ned.EncryptionMetadata.Argon2Parameters.Memory)
+		assert.Equal(t, uint32(3), ned.EncryptionMetadata.Argon2Parameters.Iterations)
+	} else {
+		assert.Equal(t, uint32(2*1024*1024), ned.EncryptionMetadata.Argon2Parameters.Memory)
+		assert.Equal(t, uint32(1), ned.EncryptionMetadata.Argon2Parameters.Iterations)
+	}
+
 	assert.Equal(t, uint8(4), ned.EncryptionMetadata.Argon2Parameters.Parallelism)
-	assert.Equal(t, uint32(1), ned.EncryptionMetadata.Argon2Parameters.Iterations)
 
 	// verify the key is valid and decrypt-able
 	var curve cert.Curve

cmd/nebula-cert/fips140enforce.go

@@ -0,0 +1,5 @@
+//go:build fips140enforce
+
+//go:debug fips140=only
+
+package main

cmd/nebula-cert/keygen.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"crypto/fips140"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -24,7 +26,7 @@ func newKeygenFlags() *keygenFlags {
 	cf.set.Usage = func() {}
 	cf.outPubPath = cf.set.String("out-pub", "", "Required: path to write the public key to")
 	cf.outKeyPath = cf.set.String("out-key", "", "Required: path to write the private key to")
-	cf.curve = cf.set.String("curve", "25519", "ECDH Curve (25519, P256)")
+	cf.curve = cf.set.String("curve", defaultCurve(), "ECDH Curve (25519, P256)")
 	cf.p11url = p11Flag(cf.set)
 	return &cf
 }
@@ -61,6 +63,9 @@ func keygen(args []string, out io.Writer, errOut io.Writer) error {
 	} else {
 		switch *cf.curve {
 		case "25519", "X25519", "Curve25519", "CURVE25519":
+			if fips140.Enforced() {
+				return errors.New("use of Curve25519 is not allowed in FIPS 140-only mode")
+			}
 			pub, rawPriv = x25519Keypair()
 			curve = cert.Curve_CURVE25519
 		case "P256":

cmd/nebula-cert/sign.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"crypto/ecdh"
+	"crypto/fips140"
 	"crypto/rand"
 	"errors"
 	"flag"
@@ -268,6 +269,10 @@ func signCert(args []string, out io.Writer, errOut io.Writer, pr PasswordReader)
 		}(p11Client)
 	}
 
+	if fips140.Enforced() && curve == cert.Curve_CURVE25519 {
+		return errors.New("use of Curve25519 is not allowed in FIPS 140-only mode")
+	}
+
 	if *sf.inPubPath != "" {
 		var pubCurve cert.Curve
 		rawPub, err := readInput("in-pub", *sf.inPubPath, &claims)

cmd/nebula-service/fips140enforce.go

@@ -0,0 +1,5 @@
+//go:build fips140enforce
+
+//go:debug fips140=only
+
+package main

cmd/nebula-service/main.go

@@ -53,7 +53,12 @@ func main() {
 	l := logging.NewLogger(os.Stdout)
 
 	if *serviceFlag != "" {
-		if err := doService(configPath, configTest, Build, serviceFlag); err != nil {
+		if *configTest {
+			fmt.Println("-test is not supported with -service, run the config test without -service")
+			os.Exit(1)
+		}
+
+		if err := doService(configPath, Build, serviceFlag); err != nil {
 			l.Error("Service command failed", "error", err)
 			os.Exit(1)
 		}
@@ -93,15 +98,14 @@ func main() {
 	}
 
 	if !*configTest {
-		wait, err := ctrl.Start()
-		if err != nil {
+		if err := ctrl.Start(); err != nil {
 			util.LogWithContextIfNeeded("Error while running", err, l)
 			os.Exit(1)
 		}
 
 		go ctrl.ShutdownBlock()
 
-		if err := wait(); err != nil {
+		if err := ctrl.Wait(); err != nil {
 			l.Error("Nebula stopped due to fatal error", "error", err)
 			os.Exit(2)
 		}

cmd/nebula-service/service.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"log"
+	"os"
 
 	"github.com/kardianos/service"
 	"github.com/slackhq/nebula"
@@ -14,7 +15,6 @@ var logger service.Logger
 
 type program struct {
 	configPath *string
-	configTest *bool
 	build      string
 	control    *nebula.Control
 }
@@ -40,22 +40,41 @@ func (p *program) Start(s service.Service) error {
 		}
 	})
 
-	p.control, err = nebula.Main(c, *p.configTest, Build, l, nil)
+	p.control, err = nebula.Main(c, false, Build, l, nil)
 	if err != nil {
 		return err
 	}
 
-	p.control.Start()
+	if err := p.control.Start(); err != nil {
+		return err
+	}
+
+	// Nebula can stop itself on a fatal packet reader error, make sure to log it if it happens.
+	go func() {
+		if err := p.control.Wait(); err != nil {
+			logger.Error(fmt.Sprintf("Nebula stopped due to fatal error: %v", err))
+			os.Exit(2)
+		}
+	}()
+
 	return nil
 }
 
 func (p *program) Stop(s service.Service) error {
 	logger.Info("Nebula service stopping.")
+	if p.control == nil {
+		return nil
+	}
+
 	p.control.Stop()
+
+	// block until nebula has fully drained before reporting stopped.
+	// error logging is handled by Start.
+	_ = p.control.Wait()
 	return nil
 }
 
-func doService(configPath *string, configTest *bool, build string, serviceFlag *string) error {
+func doService(configPath *string, build string, serviceFlag *string) error {
 	if *configPath == "" {
 		p, err := config.DefaultPath()
 		if err != nil {
@@ -73,7 +92,6 @@ func doService(configPath *string, configTest *bool, build string, serviceFlag *
 
 	prg := &program{
 		configPath: configPath,
-		configTest: configTest,
 		build:      build,
 	}
 
@@ -105,8 +123,9 @@ func doService(configPath *string, configTest *bool, build string, serviceFlag *
 	switch *serviceFlag {
 	case "run":
 		if err := s.Run(); err != nil {
-			// Route any errors to the system logger
+			// Route any errors to the system logger and report the failure
 			logger.Error(err)
+			return err
 		}
 	default:
 		if err := service.Control(s, *serviceFlag); err != nil {

cmd/nebula/close_on_timer_test.go

@@ -0,0 +1,96 @@
+//go:build linux && !android && !e2e_testing
+
+package main
+
+import (
+	"fmt"
+	"net/netip"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+	"time"
+
+	"github.com/slackhq/nebula"
+	"github.com/slackhq/nebula/cert"
+	cert_test "github.com/slackhq/nebula/cert_test"
+	"github.com/slackhq/nebula/config"
+	"github.com/slackhq/nebula/test"
+	"github.com/stretchr/testify/require"
+)
+
+// TestControlStopClosesOnTimer reproduces the dnclient lifecycle: nebula runs as
+// a library, and on a config update dnclient calls Stop() in-process to tear the
+// old instance down before starting a new one. This boots a real nebula (real
+// blocking UDP sockets, tun disabled), lets it run, then Stop()s it on a timer
+// and asserts it actually closes. If the reader goroutines parked in recvmmsg
+// don't wake on Close(), Wait() blocks forever and this fails with a goroutine
+// dump instead of relying on a process signal to unstick them.
+func TestControlStopClosesOnTimer(t *testing.T) {
+	l := test.NewLogger()
+	dir := t.TempDir()
+
+	before := time.Now().Add(-time.Hour)
+	after := time.Now().Add(time.Hour)
+	ca, _, caKey, caPEM := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, before, after, nil, nil, nil)
+	networks := []netip.Prefix{netip.MustParsePrefix("10.0.0.1/24")}
+	_, _, keyPEM, certPEM := cert_test.NewTestCert(cert.Version2, cert.Curve_CURVE25519, ca, caKey, "close-on-timer", before, after, networks, nil, nil)
+
+	caPath := filepath.Join(dir, "ca.pem")
+	certPath := filepath.Join(dir, "cert.pem")
+	keyPath := filepath.Join(dir, "key.pem")
+	require.NoError(t, os.WriteFile(caPath, caPEM, 0o600))
+	require.NoError(t, os.WriteFile(certPath, certPEM, 0o600))
+	require.NoError(t, os.WriteFile(keyPath, keyPEM, 0o600))
+
+	// tun disabled so no device/root is needed; routines: 2 so we exercise the
+	// multi-socket (SO_REUSEPORT) teardown, which is where dnclient runs.
+	configBody := fmt.Sprintf(`
+pki:
+  ca: %s
+  cert: %s
+  key: %s
+listen:
+  host: 127.0.0.1
+  port: 0
+tun:
+  disabled: true
+firewall:
+  outbound:
+    - port: any
+      proto: any
+      host: any
+  inbound:
+    - port: any
+      proto: any
+      host: any
+routines: 2
+`, caPath, certPath, keyPath)
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "config.yml"), []byte(configBody), 0o600))
+
+	c := config.NewC(l)
+	require.NoError(t, c.Load(dir))
+
+	ctrl, err := nebula.Main(c, false, "close-on-timer", l, nil)
+	require.NoError(t, err)
+	require.NoError(t, ctrl.Start())
+
+	// Run like a live nebula, then close on a timer, exactly as dnclient does.
+	<-time.NewTimer(5 * time.Second).C
+
+	stopped := make(chan struct{})
+	go func() {
+		ctrl.Stop() // closes the udp sockets (shutdown(2)) and the tun
+		ctrl.Wait() // blocks until every reader goroutine has returned
+		close(stopped)
+	}()
+
+	select {
+	case <-stopped:
+		t.Log("nebula closed cleanly on timer")
+	case <-time.After(10 * time.Second):
+		buf := make([]byte, 1<<20)
+		n := runtime.Stack(buf, true)
+		t.Fatalf("nebula did NOT close within 10s of Stop(): a blocking reader never woke\n%s", buf[:n])
+	}
+}

cmd/nebula/fips140enforce.go

@@ -0,0 +1,5 @@
+//go:build fips140enforce
+
+//go:debug fips140=only
+
+package main

cmd/nebula/main.go

@@ -84,8 +84,7 @@ func main() {
 	}
 
 	if !*configTest {
-		wait, err := ctrl.Start()
-		if err != nil {
+		if err := ctrl.Start(); err != nil {
 			util.LogWithContextIfNeeded("Error while running", err, l)
 			os.Exit(1)
 		}
@@ -93,7 +92,7 @@ func main() {
 		go ctrl.ShutdownBlock()
 		notifyReady(l)
 
-		if err := wait(); err != nil {
+		if err := ctrl.Wait(); err != nil {
 			l.Error("Nebula stopped due to fatal error", "error", err)
 			os.Exit(2)
 		}

connection_manager.go

@@ -105,11 +105,18 @@ func (cm *connectionManager) getInactivityTimeout() time.Duration {
 }
 
 func (cm *connectionManager) In(h *HostInfo) {
-	h.in.Store(true)
+	h.markIn()
 }
 
-func (cm *connectionManager) Out(h *HostInfo) {
-	h.out.Store(true)
+// OutNoRebind records outbound traffic without consuming the rebind epoch, for relayed sends: the direct path
+// to the relay consumes the edge, the via send must not.
+func (cm *connectionManager) OutNoRebind(h *HostInfo) {
+	h.markOutOnly()
+}
+
+// Out records outbound traffic and reports whether we rebound since this tunnel last sent
+func (cm *connectionManager) Out(h *HostInfo) bool {
+	return h.markOut(cm.intf.rebindEpoch.Load())
 }
 
 func (cm *connectionManager) RelayUsed(localIndex uint32) {
@@ -128,8 +135,7 @@ func (cm *connectionManager) RelayUsed(localIndex uint32) {
 // getAndResetTrafficCheck returns if there was any inbound or outbound traffic within the last tick and
 // resets the state for this local index
 func (cm *connectionManager) getAndResetTrafficCheck(h *HostInfo, now time.Time) (bool, bool) {
-	in := h.in.Swap(false)
-	out := h.out.Swap(false)
+	in, out := h.takeTraffic()
 	if in || out {
 		h.lastUsed = now
 	}
@@ -191,6 +197,27 @@ func (cm *connectionManager) doTrafficCheck(localIndex uint32, p, nb, out []byte
 	}
 
 	cm.resetRelayTrafficCheck(hostinfo)
+	cm.maintainLanes(localIndex, decision, hostinfo, now, nb, out)
+}
+
+// maintainLanes piggybacks multiport lane probing on the per-tunnel traffic
+// tick. This tick is the right place for it precisely because lanes are
+// demand-driven: a tunnel only lands here when it has traffic, which is the
+// same condition that raises lane demand.
+//
+// makeTrafficDecision returns a nil hostinfo on some keep-alive paths, so
+// re-resolve the index in that case.
+func (cm *connectionManager) maintainLanes(localIndex uint32, decision trafficDecision, hostinfo *HostInfo, now time.Time, nb, out []byte) {
+	if decision == deleteTunnel || decision == closeTunnel {
+		return
+	}
+	if hostinfo == nil {
+		hostinfo = cm.hostMap.QueryIndex(localIndex)
+		if hostinfo == nil {
+			return
+		}
+	}
+	cm.intf.probeLanes(hostinfo, now, nb, out)
 }
 
 func (cm *connectionManager) resetRelayTrafficCheck(hostinfo *HostInfo) {
@@ -323,6 +350,15 @@ func (cm *connectionManager) makeTrafficDecision(localIndex uint32, now time.Tim
 		return closeTunnel, hostinfo, nil
 	}
 
+	// The highest counter across the base session and its lanes: the lanes carry
+	// the data, so the base counter alone would sit near zero while a lane runs
+	// its keys past the nonce ceiling.
+	if hostinfo.maxMessageCounter() >= RejectAfterMessages {
+		// Send path can't encrypt a CloseTunnel notify, so just delete locally; the peer recovers via recv_error.
+		hostinfo.logger(cm.l).Error("Dropping tunnel, message counter is exhausted")
+		return deleteTunnel, hostinfo, nil
+	}
+
 	primary := cm.hostMap.Hosts[hostinfo.vpnAddrs[0]]
 	mainHostInfo := true
 	if primary != nil && primary != hostinfo {
@@ -340,7 +376,7 @@ func (cm *connectionManager) makeTrafficDecision(localIndex uint32, now time.Tim
 				"tunnelCheck", m{"state": "alive", "method": "passive"},
 			)
 		}
-		hostinfo.pendingDeletion.Store(false)
+		hostinfo.setPendingDeletion(false)
 
 		if mainHostInfo {
 			decision = tryRehandshake
@@ -363,7 +399,7 @@ func (cm *connectionManager) makeTrafficDecision(localIndex uint32, now time.Tim
 		return decision, hostinfo, primary
 	}
 
-	if hostinfo.pendingDeletion.Load() {
+	if hostinfo.isPendingDeletion() {
 		// We have already sent a test packet and nothing was returned, this hostinfo is dead
 		hostinfo.logger(cm.l).Info("Tunnel status",
 			"tunnelCheck", m{"state": "dead", "method": "active"},
@@ -414,7 +450,7 @@ func (cm *connectionManager) makeTrafficDecision(localIndex uint32, now time.Tim
 		}
 	}
 
-	hostinfo.pendingDeletion.Store(true)
+	hostinfo.setPendingDeletion(true)
 	cm.trafficTimer.Add(hostinfo.localIndexId, cm.pendingDeletionInterval)
 	return decision, hostinfo, nil
 }
@@ -425,6 +461,7 @@ func (cm *connectionManager) isInactive(hostinfo *HostInfo, now time.Time) (time
 		return 0, false
 	}
 
+	// Lane traffic is this hostinfo's traffic, so lastUsed already covers it.
 	inactiveDuration := now.Sub(hostinfo.lastUsed)
 	if inactiveDuration < cm.getInactivityTimeout() {
 		// It's not considered inactive
@@ -448,6 +485,11 @@ func (cm *connectionManager) shouldSwapPrimary(current *HostInfo) bool {
 		return false
 	}
 
+	if current.maxMessageCounter() >= RehandshakeAfterMessages {
+		// This tunnel is being rolled for counter exhaustion, never swap back onto its spent key.
+		return false
+	}
+
 	crt := cm.intf.pki.getCertState().getCertificate(current.ConnectionState.myCert.Version())
 	if crt == nil {
 		//my cert was reloaded away. We should definitely swap from this tunnel
@@ -544,6 +586,15 @@ func (cm *connectionManager) tryRehandshake(hostinfo *HostInfo) {
 			"reason", "current cert version < pki.initiatingVersion",
 		)
 
+		cm.intf.handshakeManager.StartHandshake(hostinfo.vpnAddrs[0], nil)
+		return
+	}
+	if hostinfo.maxMessageCounter() >= RehandshakeAfterMessages {
+		cm.l.Info("Re-handshaking with remote",
+			"vpnAddrs", hostinfo.vpnAddrs,
+			"reason", "message counter rehandshake threshold reached",
+		)
+
 		cm.intf.handshakeManager.StartHandshake(hostinfo.vpnAddrs[0], nil)
 		return
 	}

connection_manager_test.go

@@ -25,6 +25,7 @@ func newTestLighthouse() *LightHouse {
 	lighthouses := []netip.Addr{}
 	staticList := map[netip.Addr]struct{}{}
 
+	lh.localAddrsFn = func(*LocalAllowList) []netip.Addr { return nil }
 	lh.lighthouses.Store(&lighthouses)
 	lh.staticList.Store(&staticList)
 
@@ -85,25 +86,25 @@ func Test_NewConnectionManagerTest(t *testing.T) {
 	// We saw traffic out to vpnIp
 	nc.Out(hostinfo)
 	nc.In(hostinfo)
-	assert.False(t, hostinfo.pendingDeletion.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
-	assert.True(t, hostinfo.out.Load())
-	assert.True(t, hostinfo.in.Load())
+	assert.True(t, hostinfo.sentSinceCheck())
+	assert.True(t, (hostinfo.state.Load()&stateIn != 0))
 
 	// Do a traffic check tick, should not be pending deletion but should not have any in/out packets recorded
 	nc.doTrafficCheck(hostinfo.localIndexId, p, nb, out, time.Now())
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 
 	// Do another traffic check tick, this host should be pending deletion now
 	nc.Out(hostinfo)
-	assert.True(t, hostinfo.out.Load())
+	assert.True(t, hostinfo.sentSinceCheck())
 	nc.doTrafficCheck(hostinfo.localIndexId, p, nb, out, time.Now())
-	assert.True(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.True(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 
@@ -167,37 +168,110 @@ func Test_NewConnectionManagerTest2(t *testing.T) {
 	// We saw traffic out to vpnIp
 	nc.Out(hostinfo)
 	nc.In(hostinfo)
-	assert.True(t, hostinfo.in.Load())
-	assert.True(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.pendingDeletion.Load())
+	assert.True(t, (hostinfo.state.Load()&stateIn != 0))
+	assert.True(t, hostinfo.sentSinceCheck())
+	assert.False(t, hostinfo.isPendingDeletion())
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
 
 	// Do a traffic check tick, should not be pending deletion but should not have any in/out packets recorded
 	nc.doTrafficCheck(hostinfo.localIndexId, p, nb, out, time.Now())
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 
 	// Do another traffic check tick, this host should be pending deletion now
 	nc.Out(hostinfo)
 	nc.doTrafficCheck(hostinfo.localIndexId, p, nb, out, time.Now())
-	assert.True(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.True(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 
 	// We saw traffic, should no longer be pending deletion
 	nc.In(hostinfo)
 	nc.doTrafficCheck(hostinfo.localIndexId, p, nb, out, time.Now())
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 }
 
+func Test_NewConnectionManager_CounterLimits(t *testing.T) {
+	l := test.NewLogger()
+	localrange := netip.MustParsePrefix("10.1.1.1/24")
+	vpnIp := netip.MustParseAddr("172.1.1.2")
+	preferredRanges := []netip.Prefix{localrange}
+
+	// Very incomplete mock objects
+	hostMap := newHostMap(l)
+	hostMap.preferredRanges.Store(&preferredRanges)
+
+	cs := &CertState{
+		initiatingVersion: cert.Version1,
+		privateKey:        []byte{},
+		v1Cert:            &dummyCert{version: cert.Version1},
+		v1Credential:      nil,
+	}
+
+	lh := newTestLighthouse()
+	ifce := &Interface{
+		hostMap:          hostMap,
+		inside:           &overlaytest.NoopTun{},
+		outside:          &udp.NoopConn{},
+		firewall:         &Firewall{},
+		lightHouse:       lh,
+		pki:              &PKI{},
+		myVpnAddrs:       []netip.Addr{netip.MustParseAddr("172.1.1.1")}, // sorts below vpnIp so shouldSwapPrimary can proceed
+		handshakeManager: NewHandshakeManager(l, hostMap, lh, &udp.NoopConn{}, defaultHandshakeConfig),
+		l:                l,
+	}
+	ifce.pki.cs.Store(cs)
+
+	conf := config.NewC(test.NewLogger())
+	punchy := NewPunchyFromConfig(test.NewLogger(), conf, nil)
+	nc := newConnectionManagerFromConfig(test.NewLogger(), conf, hostMap, punchy)
+	nc.intf = ifce
+
+	hostinfo := &HostInfo{
+		vpnAddrs:      []netip.Addr{vpnIp},
+		localIndexId:  1099,
+		remoteIndexId: 9901,
+	}
+	hostinfo.ConnectionState = &ConnectionState{
+		myCert: &dummyCert{version: cert.Version1},
+	}
+	nc.hostMap.unlockedAddHostInfo(hostinfo, ifce)
+
+	// Below the rehandshake threshold, no handshake is started
+	hostinfo.ConnectionState.messageCounter.Store(RehandshakeAfterMessages - 1)
+	nc.tryRehandshake(hostinfo)
+	assert.Nil(t, ifce.handshakeManager.QueryVpnAddr(vpnIp))
+
+	// A tunnel on its current cert would normally swap to primary
+	assert.True(t, nc.shouldSwapPrimary(hostinfo))
+
+	// At the rehandshake threshold, a new handshake is started
+	hostinfo.ConnectionState.messageCounter.Store(RehandshakeAfterMessages)
+	nc.tryRehandshake(hostinfo)
+	assert.NotNil(t, ifce.handshakeManager.QueryVpnAddr(vpnIp))
+
+	// An exhausted tunnel being rolled must never swap back to primary onto its spent key
+	assert.False(t, nc.shouldSwapPrimary(hostinfo))
+
+	// Still below the reject limit, the tunnel stays up
+	nc.In(hostinfo)
+	decision, _, _ := nc.makeTrafficDecision(hostinfo.localIndexId, time.Now())
+	assert.Equal(t, tryRehandshake, decision)
+
+	// At the reject limit, the tunnel is deleted locally without a doomed CloseTunnel notify
+	hostinfo.ConnectionState.messageCounter.Store(RejectAfterMessages)
+	decision, _, _ = nc.makeTrafficDecision(hostinfo.localIndexId, time.Now())
+	assert.Equal(t, deleteTunnel, decision)
+}
+
 func Test_NewConnectionManager_DisconnectInactive(t *testing.T) {
 	l := test.NewLogger()
 	localrange := netip.MustParsePrefix("10.1.1.1/24")
@@ -252,31 +326,31 @@ func Test_NewConnectionManager_DisconnectInactive(t *testing.T) {
 	// Do a traffic check tick, in and out should be cleared but should not be pending deletion
 	nc.Out(hostinfo)
 	nc.In(hostinfo)
-	assert.True(t, hostinfo.out.Load())
-	assert.True(t, hostinfo.in.Load())
+	assert.True(t, hostinfo.sentSinceCheck())
+	assert.True(t, (hostinfo.state.Load()&stateIn != 0))
 
 	now := time.Now()
 	decision, _, _ := nc.makeTrafficDecision(hostinfo.localIndexId, now)
 	assert.Equal(t, tryRehandshake, decision)
 	assert.Equal(t, now, hostinfo.lastUsed)
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 
 	decision, _, _ = nc.makeTrafficDecision(hostinfo.localIndexId, now.Add(time.Second*5))
 	assert.Equal(t, doNothing, decision)
 	assert.Equal(t, now, hostinfo.lastUsed)
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 
 	// Do another traffic check tick, should still not be pending deletion
 	decision, _, _ = nc.makeTrafficDecision(hostinfo.localIndexId, now.Add(time.Second*10))
 	assert.Equal(t, doNothing, decision)
 	assert.Equal(t, now, hostinfo.lastUsed)
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 
@@ -284,9 +358,9 @@ func Test_NewConnectionManager_DisconnectInactive(t *testing.T) {
 	decision, _, _ = nc.makeTrafficDecision(hostinfo.localIndexId, now.Add(time.Minute*10))
 	assert.Equal(t, closeTunnel, decision)
 	assert.Equal(t, now, hostinfo.lastUsed)
-	assert.False(t, hostinfo.pendingDeletion.Load())
-	assert.False(t, hostinfo.out.Load())
-	assert.False(t, hostinfo.in.Load())
+	assert.False(t, hostinfo.isPendingDeletion())
+	assert.False(t, hostinfo.sentSinceCheck())
+	assert.False(t, (hostinfo.state.Load()&stateIn != 0))
 	assert.Contains(t, nc.hostMap.Indexes, hostinfo.localIndexId)
 	assert.Contains(t, nc.hostMap.Hosts, hostinfo.vpnAddrs[0])
 }

connection_state.go

@@ -1,16 +1,41 @@
 package nebula
 
 import (
+	"crypto/hkdf"
+	"crypto/sha256"
 	"encoding/json"
+	"fmt"
+	"log/slog"
+	"strconv"
 	"sync"
 	"sync/atomic"
 
 	"github.com/slackhq/nebula/cert"
 	"github.com/slackhq/nebula/handshake"
+	"github.com/slackhq/nebula/header"
 	"github.com/slackhq/nebula/noiseutil"
 )
 
-const ReplayWindow = 1024
+const (
+	ReplayWindow = 8192
+
+	// RehandshakeAfterMessages rolls keys inside the AES-GCM data-volume margin (~2^-36 advantage at 64KB frames).
+	RehandshakeAfterMessages = uint64(1) << 34
+
+	// RejectAfterMessages is the nonce ceiling enforced by noiseutil; a tunnel here is deleted locally, not notified.
+	RejectAfterMessages = noiseutil.RejectAfterMessages
+)
+
+// RehandshakeAfterMessages must stay below RejectAfterMessages so tunnels roll before the hard send stop.
+const _ = RejectAfterMessages - RehandshakeAfterMessages
+
+// sessionEpoch hands out a receiver-local ordinal to every ConnectionState at creation. The RX
+// staging sort (overlay/batch) orders packets by (epoch, message counter). A re-handshake never
+// rekeys an existing tunnel; it brings up a new hostinfo and ConnectionState with a counter space
+// starting near zero, while the old tunnel keeps decrypting until torn down. During that cutover
+// one flush batch can hold packets from both tunnels, and the epoch keeps the old tunnel's
+// packets sorted first.
+var sessionEpoch atomic.Uint64
 
 type ConnectionState struct {
 	eKey           noiseutil.CipherState
@@ -20,14 +45,22 @@ type ConnectionState struct {
 	initiator      bool
 	messageCounter atomic.Uint64
 	window         *Bits
+	decryptLock    sync.Mutex
 	writeLock      sync.Mutex
+	// epoch is this session's sessionEpoch ordinal. Immutable after creation.
+	epoch uint64
 }
 
 // newConnectionStateFromResult builds a fully-populated ConnectionState from a
 // completed handshake.Result. It seeds messageCounter and the replay window so
 // that the post-handshake message indices already used on the wire don't count
 // as missed traffic in the data plane.
-func newConnectionStateFromResult(r *handshake.Result) *ConnectionState {
+func newConnectionStateFromResult(r *handshake.Result) (*ConnectionState, error) {
+	// Refuse a MessageIndex too big for the replay window: it can only be a bug, and would spin the seed loop below.
+	if r.MessageIndex >= ReplayWindow {
+		return nil, fmt.Errorf("handshake message index %d exceeds replay window", r.MessageIndex)
+	}
+
 	ci := &ConnectionState{
 		myCert:    r.MyCert,
 		initiator: r.Initiator,
@@ -35,12 +68,60 @@ func newConnectionStateFromResult(r *handshake.Result) *ConnectionState {
 		eKey:      noiseutil.NewCipherState(r.EKey, r.Cipher),
 		dKey:      noiseutil.NewCipherState(r.DKey, r.Cipher),
 		window:    NewBits(ReplayWindow),
+		epoch:     sessionEpoch.Add(1),
 	}
 	ci.messageCounter.Add(r.MessageIndex)
 	for i := uint64(1); i <= r.MessageIndex; i++ {
 		ci.window.Update(nil, i)
 	}
-	return ci
+	return ci, nil
+}
+
+// newLaneConnectionState derives multiport lane s's session from the base
+// tunnel's material. Each key is an HKDF expansion of the base tunnel's matching
+// key, labelled with the lane index, so the pair stays matched with no extra
+// negotiation: Noise leaves our send key equal to the peer's receive key, and
+// expanding both with the same label preserves that.
+//
+// The lane gets its own counter and replay window starting from zero. No
+// handshake messages were spent on it, so unlike the base session there is
+// nothing to seed.
+func newLaneConnectionState(m *laneMaterial, lane uint8) (*ConnectionState, error) {
+	if lane == 0 {
+		return nil, fmt.Errorf("lane 0 is the base session")
+	}
+
+	eKey, err := deriveLaneKey(m.eKey, lane)
+	if err != nil {
+		return nil, err
+	}
+	dKey, err := deriveLaneKey(m.dKey, lane)
+	if err != nil {
+		return nil, err
+	}
+
+	return &ConnectionState{
+		myCert:    m.myCert,
+		initiator: m.initiator,
+		peerCert:  m.peerCert,
+		eKey:      noiseutil.NewCipherStateFromKey(eKey, m.cipher),
+		dKey:      noiseutil.NewCipherStateFromKey(dKey, m.cipher),
+		window:    NewBits(ReplayWindow),
+		epoch:     sessionEpoch.Add(1),
+	}, nil
+}
+
+// deriveLaneKey expands a base tunnel key into the key for one lane.
+func deriveLaneKey(base [32]byte, lane uint8) ([32]byte, error) {
+	var out [32]byte
+	// The base key is already unique to this tunnel and direction, so the lane
+	// index is the only thing that needs to vary; no salt is required.
+	k, err := hkdf.Key(sha256.New, base[:], nil, laneKeyInfo+" "+strconv.Itoa(int(lane)), len(out))
+	if err != nil {
+		return out, err
+	}
+	copy(out[:], k)
+	return out, nil
 }
 
 func (cs *ConnectionState) MarshalJSON() ([]byte, error) {
@@ -51,6 +132,76 @@ func (cs *ConnectionState) MarshalJSON() ([]byte, error) {
 	})
 }
 
+// NextMessageCounter reserves the next 1-based counter; RejectAfterMessages is the first we refuse, pinned to not wrap.
+func (cs *ConnectionState) NextMessageCounter() (uint64, bool) {
+	c := cs.messageCounter.Add(1)
+	if c >= RejectAfterMessages {
+		cs.messageCounter.Store(RejectAfterMessages)
+		return c, false
+	}
+	return c, true
+}
+
 func (cs *ConnectionState) Curve() cert.Curve {
 	return cs.myCert.Curve()
 }
+
+func (cs *ConnectionState) Decrypt(l *slog.Logger, messageCounter uint64, packet []byte, nb []byte) ([]byte, error) {
+	cs.decryptLock.Lock()
+	result := cs.window.Check(l, messageCounter)
+	cs.decryptLock.Unlock()
+	if !result {
+		return nil, ErrAlreadySeen
+	}
+
+	out, err := cs.dKey.DecryptDanger(packet[header.Len:header.Len], packet[:header.Len], packet[header.Len:], messageCounter, nb)
+	if err != nil {
+		return nil, err
+	}
+
+	cs.decryptLock.Lock()
+	result = cs.window.Update(l, messageCounter)
+	cs.decryptLock.Unlock()
+	if !result {
+		return nil, ErrAlreadySeen
+	}
+	return out, nil
+}
+
+// noteSeen records a counter that some other session for the same keys already
+// accepted, so a packet doesn't become replayable just because the session that
+// decrypted it was thrown away. See laneSet.installSession, its only caller.
+func (cs *ConnectionState) noteSeen(l *slog.Logger, messageCounter uint64) {
+	cs.decryptLock.Lock()
+	cs.window.Update(l, messageCounter)
+	cs.decryptLock.Unlock()
+}
+
+func (cs *ConnectionState) VerifyRelay(l *slog.Logger, messageCounter uint64, packet []byte, nb []byte) error {
+	cs.decryptLock.Lock()
+	result := cs.window.Check(l, messageCounter)
+	cs.decryptLock.Unlock()
+	if !result {
+		return ErrAlreadySeen
+	}
+
+	// The entire body is sent as AD, not encrypted.
+	// The packet consists of a 16-byte parsed Nebula header, Associated Data-protected payload, and a trailing 16-byte AEAD signature value.
+	// The packet is guaranteed to be at least 16 bytes at this point, b/c it got past the h.Parse() call above. If it's
+	// otherwise malformed (meaning, there is no trailing 16 byte AEAD value), then this will result in at worst a 0-length slice
+	// which will gracefully fail in the DecryptDanger call.
+	signedPayload := packet[:len(packet)-cs.dKey.Overhead()]
+	signatureValue := packet[len(packet)-cs.dKey.Overhead():]
+	_, err := cs.dKey.DecryptDanger(nil, signedPayload, signatureValue, messageCounter, nb)
+	if err != nil {
+		return err
+	}
+
+	cs.decryptLock.Lock()
+	result = cs.window.Update(l, messageCounter)
+	cs.decryptLock.Unlock()
+	if !result {
+		return ErrAlreadySeen
+	}
+	return nil
+}

connection_state_test.go

@@ -6,10 +6,13 @@ import (
 	"time"
 
 	"github.com/flynn/noise"
+	"github.com/rcrowley/go-metrics"
 	"github.com/slackhq/nebula/cert"
 	ct "github.com/slackhq/nebula/cert_test"
 	"github.com/slackhq/nebula/handshake"
 	"github.com/slackhq/nebula/header"
+	"github.com/slackhq/nebula/test"
+	"github.com/slackhq/nebula/udp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -55,6 +58,7 @@ func runTestHandshake(t *testing.T) (initR, respR *handshake.Result) {
 		cert.Version2, initCreds, verifier,
 		func() (uint32, error) { return 1000, nil },
 		true, header.HandshakeIXPSK0,
+		nil,
 	)
 	require.NoError(t, err)
 
@@ -62,6 +66,7 @@ func runTestHandshake(t *testing.T) (initR, respR *handshake.Result) {
 		cert.Version2, respCreds, verifier,
 		func() (uint32, error) { return 2000, nil },
 		false, header.HandshakeIXPSK0,
+		nil,
 	)
 	require.NoError(t, err)
 
@@ -79,11 +84,77 @@ func runTestHandshake(t *testing.T) (initR, respR *handshake.Result) {
 	return initR, respR
 }
 
+func TestConnectionState_NextMessageCounter(t *testing.T) {
+	cs := &ConnectionState{}
+	cs.messageCounter.Store(RejectAfterMessages - 2)
+
+	c, ok := cs.NextMessageCounter()
+	assert.True(t, ok)
+	assert.Equal(t, RejectAfterMessages-1, c)
+
+	// Hitting the limit refuses and pins the counter there
+	c, ok = cs.NextMessageCounter()
+	assert.False(t, ok)
+	assert.Equal(t, RejectAfterMessages, c)
+	assert.Equal(t, RejectAfterMessages, cs.messageCounter.Load())
+
+	// Continued send attempts stay refused and the counter never wraps
+	for i := 0; i < 10; i++ {
+		_, ok = cs.NextMessageCounter()
+		assert.False(t, ok)
+	}
+	assert.Equal(t, RejectAfterMessages, cs.messageCounter.Load())
+}
+
+// TestSendNoMetricsDropsExhausted drives the send path to the exhausted drop; metric and out flag prove it.
+func TestSendNoMetricsDropsExhausted(t *testing.T) {
+	initR, _ := runTestHandshake(t)
+	ci, err := newConnectionStateFromResult(initR)
+	require.NoError(t, err)
+	ci.messageCounter.Store(RejectAfterMessages - 1)
+
+	f := &Interface{l: test.NewLogger(), messageMetrics: &MessageMetrics{txExhausted: metrics.NewCounter()}}
+	hostinfo := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("10.0.0.1")}, ConnectionState: ci}
+
+	f.sendNoMetrics(header.Message, 0, ci, hostinfo, netip.AddrPort{}, []byte{}, make([]byte, 12), make([]byte, mtu), 0)
+
+	// The crossing send is refused: it records an exhaustion drop and never reaches connectionManager.Out.
+	assert.Equal(t, int64(1), f.messageMetrics.txExhausted.Count())
+	assert.False(t, hostinfo.sentSinceCheck())
+}
+
+// TestSendNoMetricsCloseTunnelKeepsRebindEpoch pins that a closing tunnel does not consume a rebind, a later
+// packet on a re-established tunnel still needs that edge to trigger the far-side punch.
+func TestSendNoMetricsCloseTunnelKeepsRebindEpoch(t *testing.T) {
+	initR, _ := runTestHandshake(t)
+	ci, err := newConnectionStateFromResult(initR)
+	require.NoError(t, err)
+
+	f := &Interface{
+		l:                 test.NewLogger(),
+		messageMetrics:    &MessageMetrics{txExhausted: metrics.NewCounter()},
+		writers:           []udp.Conn{udp.NoopConn{}},
+		connectionManager: &connectionManager{},
+	}
+	hostinfo := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("10.0.0.1")}, ConnectionState: ci}
+
+	// Tunnel is on epoch 0, then we rebind.
+	hostinfo.markOut(0)
+	f.rebindEpoch.Add(1)
+
+	remote := netip.MustParseAddrPort("10.0.0.2:4242")
+	f.sendNoMetrics(header.CloseTunnel, 0, ci, hostinfo, remote, []byte{}, make([]byte, 12), make([]byte, mtu), 0)
+
+	// markOut at the new epoch still reports the move, so the edge was preserved.
+	assert.True(t, hostinfo.markOut(1), "a CloseTunnel send must not consume the rebind epoch")
+}
+
 func TestNewConnectionStateFromResult(t *testing.T) {
 	initR, respR := runTestHandshake(t)
 
 	t.Run("initiator", func(t *testing.T) {
-		ci := newConnectionStateFromResult(initR)
+		ci, err := newConnectionStateFromResult(initR)
+		require.NoError(t, err)
 		assert.True(t, ci.initiator)
 		assert.Equal(t, initR.MyCert, ci.myCert)
 		assert.Equal(t, initR.RemoteCert, ci.peerCert)
@@ -102,8 +173,17 @@ func TestNewConnectionStateFromResult(t *testing.T) {
 		assert.True(t, ci.window.Check(nil, 3), "counter 3 must not be pre-seeded")
 	})
 
+	t.Run("message index too large is refused", func(t *testing.T) {
+		bad := *initR
+		bad.MessageIndex = ReplayWindow
+		ci, err := newConnectionStateFromResult(&bad)
+		require.Error(t, err)
+		assert.Nil(t, ci)
+	})
+
 	t.Run("responder", func(t *testing.T) {
-		ci := newConnectionStateFromResult(respR)
+		ci, err := newConnectionStateFromResult(respR)
+		require.NoError(t, err)
 		assert.False(t, ci.initiator)
 		assert.Equal(t, respR.MyCert, ci.myCert)
 		assert.Equal(t, respR.RemoteCert, ci.peerCert)

control.go

@@ -53,6 +53,7 @@ type Control struct {
 	statsStart             func()
 	dnsStart               func()
 	lighthouseStart        func()
+	networkChangeStart     func(rebind func())
 	connectionManagerStart func(context.Context)
 }
 
@@ -66,32 +67,42 @@ type ControlHostInfo struct {
 	CurrentRemote          netip.AddrPort   `json:"currentRemote"`
 	CurrentRelaysToMe      []netip.Addr     `json:"currentRelaysToMe"`
 	CurrentRelaysThroughMe []netip.Addr     `json:"currentRelaysThroughMe"`
+	Lanes                  []ControlLane    `json:"lanes,omitempty"`
+}
+
+// ControlLane reports one multiport lane of a tunnel. Only lanes we may send on
+// are listed; receive-only lanes have no state worth showing.
+type ControlLane struct {
+	Index          uint8          `json:"index"`
+	Up             bool           `json:"up"`
+	Remote         netip.AddrPort `json:"remote,omitempty"`
+	MessageCounter uint64         `json:"messageCounter"`
 }
 
 // Start actually runs nebula, this is a nonblocking call.
-// The returned function blocks until nebula has fully stopped and returns the
-// first fatal reader error (if any). A nil error means nebula shut down
-// gracefully; a non-nil error means a reader hit an unexpected failure that
-// triggered the shutdown.
-func (c *Control) Start() (func() error, error) {
+// Use Wait to block until nebula has fully stopped and to learn whether a fatal reader error caused the shutdown.
+func (c *Control) Start() error {
 	c.stateLock.Lock()
 	defer c.stateLock.Unlock()
 	switch c.state {
 	case StateReady:
 		//yay!
 	case StateStopped, StateStopping:
-		return nil, ErrAlreadyStopped
+		return ErrAlreadyStopped
 	case StateStarted:
-		return nil, ErrAlreadyStarted
+		return ErrAlreadyStarted
 	default:
-		return nil, ErrUnknownState
+		return ErrUnknownState
 	}
 
 	// Activate the interface
 	err := c.f.activate()
 	if err != nil {
+		// Cancel before Close so a caller returning from Wait always observes a dead Context
+		c.cancel()
+		_ = c.f.Close()
 		c.state = StateStopped
-		return nil, err
+		return err
 	}
 
 	// Call all the delayed funcs that waited patiently for the interface to be created.
@@ -104,6 +115,9 @@ func (c *Control) Start() (func() error, error) {
 	if c.dnsStart != nil {
 		go c.dnsStart()
 	}
+	if c.networkChangeStart != nil {
+		go c.networkChangeStart(c.RebindUDPServer)
+	}
 	if c.connectionManagerStart != nil {
 		go c.connectionManagerStart(c.ctx)
 	}
@@ -111,16 +125,12 @@ func (c *Control) Start() (func() error, error) {
 		c.lighthouseStart()
 	}
 
-	c.f.triggerShutdown = c.Stop
+	c.f.triggerShutdown = func() { go c.Stop() }
 
 	// Start reading packets.
-	out, err := c.f.run()
-	if err != nil {
-		c.state = StateStopped
-		return nil, err
-	}
+	c.f.run()
 	c.state = StateStarted
-	return out, nil
+	return nil
 }
 
 func (c *Control) State() RunState {
@@ -133,10 +143,26 @@ func (c *Control) Context() context.Context {
 	return c.ctx
 }
 
-// Stop is a non-blocking call that signals nebula to close all tunnels and shut down
+// Stop tears nebula down, closing all tunnels and releasing everything it holds.
+// Use Wait to block until the shutdown has completed.
+// A Control that has been stopped cannot be started again, Start will return ErrAlreadyStopped.
 func (c *Control) Stop() {
 	c.stateLock.Lock()
-	if c.state != StateStarted {
+	switch c.state {
+	case StateStarted:
+		// Fall through to the full teardown below
+
+	case StateReady:
+		// Never started
+		c.cancel()
+		c.state = StateStopped
+		if err := c.f.Close(); err != nil {
+			c.l.Error("Close interface failed", "error", err)
+		}
+		c.stateLock.Unlock()
+		return
+
+	default:
 		c.stateLock.Unlock()
 		// We are stopping or stopped already
 		return
@@ -145,19 +171,26 @@ func (c *Control) Stop() {
 	c.state = StateStopping
 	c.stateLock.Unlock()
 
-	// Stop the handshakeManager (and other services), to prevent new tunnels from
-	// being created while we're shutting them all down.
+	// Closing tunnels can be slow with a large hostmap, don't hold the lock for it
 	c.cancel()
-
 	c.CloseAllTunnels(false)
+
+	c.stateLock.Lock()
+	c.state = StateStopped
 	if err := c.f.Close(); err != nil {
 		c.l.Error("Close interface failed", "error", err)
 	}
-	c.stateLock.Lock()
-	c.state = StateStopped
 	c.stateLock.Unlock()
 }
 
+// Wait blocks until nebula has fully stopped, either via Stop or an internal fatal error,
+// and returns the first fatal packet reader error if there was one.
+// It is safe to call from multiple goroutines and at any point in the lifecycle,
+// but a Wait on a Control that is never started and never stopped will block forever.
+func (c *Control) Wait() error {
+	return c.f.wait()
+}
+
 // ShutdownBlock will listen for and block on term and interrupt signals, calling Control.Stop() once signalled
 func (c *Control) ShutdownBlock() {
 	sigChan := make(chan os.Signal, 1)
@@ -170,15 +203,31 @@ func (c *Control) ShutdownBlock() {
 	c.Stop()
 }
 
-// RebindUDPServer asks the UDP listener to rebind it's listener. Mainly used on mobile clients when interfaces change
+// RebindUDPServer asks the UDP listener to rebind it's listener. Mainly used on mobile clients when interfaces change.
 func (c *Control) RebindUDPServer() {
-	_ = c.f.outside.Rebind()
+	c.stateLock.Lock()
+	defer c.stateLock.Unlock()
+
+	if c.state != StateStarted {
+		return
+	}
+
+	// Every socket needs rebinding, not just the base: with multiport each one is bound to its own lane port, and
+	// even without it the surplus SO_REUSEPORT sockets stay pinned to the interface we came up on otherwise.
+	//
+	// A failure here means we are likely still pinned to the interface we came up on, so the rest of this is
+	// unlikely to help. Say so instead of silently carrying on as if we rebound.
+	for i, w := range c.f.writers {
+		if err := w.Rebind(); err != nil {
+			c.l.Error("Failed to rebind udp socket", "error", err, "writer", i)
+		}
+	}
 
 	// Trigger a lighthouse update, useful for mobile clients that should have an update interval of 0
 	c.f.lightHouse.SendUpdate()
 
 	// Let the main interface know that we rebound so that underlying tunnels know to trigger punches from their remotes
-	c.f.rebindCount++
+	c.f.rebindEpoch.Add(1)
 }
 
 // ListHostmapHosts returns details about the actual or pending (handshaking) hostmap by vpn ip
@@ -351,6 +400,7 @@ func copyHostInfo(h *HostInfo, preferredRanges []netip.Prefix) ControlHostInfo {
 		CurrentRelaysToMe:      h.relayState.CopyRelayIps(),
 		CurrentRelaysThroughMe: h.relayState.CopyRelayForIps(),
 		CurrentRemote:          h.GetRemote(),
+		Lanes:                  copyLanes(h),
 	}
 
 	for i, a := range h.vpnAddrs {
@@ -368,6 +418,30 @@ func copyHostInfo(h *HostInfo, preferredRanges []netip.Prefix) ControlHostInfo {
 	return chi
 }
 
+// copyLanes snapshots the sendable multiport lanes of a tunnel, or nil when it
+// has none. txAddr is the lane's gate as well as its destination, so a nil load
+// is exactly "this lane is down and its routine is riding the base tunnel".
+func copyLanes(h *HostInfo) []ControlLane {
+	ls := h.lanes
+	if ls == nil || ls.txLanes < 2 {
+		return nil
+	}
+
+	lanes := make([]ControlLane, 0, ls.txLanes-1)
+	for s := 1; s < ls.txLanes; s++ {
+		l := ControlLane{Index: uint8(s)}
+		if addr := ls.txAddr[s].Load(); addr != nil {
+			l.Up = true
+			l.Remote = *addr
+		}
+		if cs := ls.sessions[s].Load(); cs != nil {
+			l.MessageCounter = cs.messageCounter.Load()
+		}
+		lanes = append(lanes, l)
+	}
+	return lanes
+}
+
 func listHostMapHosts(hl controlHostLister) []ControlHostInfo {
 	hosts := make([]ControlHostInfo, 0)
 	pr := hl.GetPreferredRanges()

control_lifecycle_test.go

@@ -0,0 +1,309 @@
+package nebula
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net/netip"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/gaissmai/bart"
+	"github.com/slackhq/nebula/config"
+	"github.com/slackhq/nebula/overlay/batch"
+	"github.com/slackhq/nebula/overlay/tio"
+	"github.com/slackhq/nebula/routing"
+	"github.com/slackhq/nebula/test"
+	"github.com/slackhq/nebula/udp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type fakeDevice struct {
+	closeOnce sync.Once
+	closedCh  chan struct{}
+	closed    bool
+}
+
+func newFakeDevice() *fakeDevice {
+	return &fakeDevice{closedCh: make(chan struct{})}
+}
+
+// Read blocks until Close like a real tun with no traffic, then reports EOF
+// the same way a closed device does
+func (d *fakeDevice) Read() ([]tio.Packet, error) {
+	<-d.closedCh
+	return nil, io.EOF
+}
+
+func (d *fakeDevice) Write(p []byte) (int, error) { return len(p), nil }
+
+func (d *fakeDevice) Close() error {
+	d.closeOnce.Do(func() {
+		d.closed = true
+		close(d.closedCh)
+	})
+	return nil
+}
+
+func (d *fakeDevice) Activate() error                       { return nil }
+func (d *fakeDevice) Networks() []netip.Prefix              { return nil }
+func (d *fakeDevice) Name() string                          { return "fake" }
+func (d *fakeDevice) RoutesFor(netip.Addr) routing.Gateways { return nil }
+
+func (d *fakeDevice) Queues(int) ([]tio.Queue, error) { return []tio.Queue{d}, nil }
+
+// newReadyControl hand-builds the minimum Control that Main would have
+// produced right before Start, including the construction token NewInterface
+// takes so waiters block until Close releases the resources
+func newReadyControl(t *testing.T) (*Control, *fakeDevice, *fakeConn) {
+	l := test.NewLogger()
+	dev := newFakeDevice()
+	conn := &fakeConn{}
+	ctx, cancel := context.WithCancel(context.Background())
+
+	myVpnNet := netip.MustParsePrefix("10.128.0.1/16")
+	nt := new(bart.Lite)
+	nt.Insert(myVpnNet)
+	cs := &CertState{
+		myVpnNetworks:      []netip.Prefix{myVpnNet},
+		myVpnNetworksTable: nt,
+	}
+	lh, err := NewLightHouseFromConfig(ctx, l, config.NewC(l), cs, nil, nil)
+	require.NoError(t, err)
+
+	f := &Interface{
+		ctx:        ctx,
+		inside:     dev,
+		outside:    conn,
+		writers:    []udp.Conn{conn},
+		batchers:   make([]*batch.MultiCoalescer, 1),
+		routines:   1,
+		hostMap:    newHostMap(l),
+		lightHouse: lh,
+		l:          l,
+	}
+	f.wg.Add(1)
+
+	return &Control{
+		state:  StateReady,
+		f:      f,
+		l:      l,
+		ctx:    ctx,
+		cancel: cancel,
+	}, dev, conn
+}
+
+func TestControl_StopBeforeStart(t *testing.T) {
+	c, dev, conn := newReadyControl(t)
+
+	// A Stop on a never started control must release everything Main acquired
+	c.Stop()
+	assert.Equal(t, StateStopped, c.State())
+	assert.True(t, dev.closed, "the tun device should have been closed")
+	assert.True(t, conn.closed, "the udp socket should have been closed")
+	require.ErrorIs(t, c.ctx.Err(), context.Canceled, "the service context should have been cancelled")
+
+	// Wait must return promptly now that the resources are released
+	require.NoError(t, c.Wait())
+
+	// A stopped control can never be started
+	err := c.Start()
+	require.ErrorIs(t, err, ErrAlreadyStopped)
+
+	// A second Stop is a harmless no-op
+	c.Stop()
+	assert.Equal(t, StateStopped, c.State())
+	require.NoError(t, c.Wait())
+}
+
+func TestControl_WaitBlocksUntilStop(t *testing.T) {
+	c, _, _ := newReadyControl(t)
+
+	done := make(chan error, 1)
+	go func() { done <- c.Wait() }()
+
+	select {
+	case <-done:
+		t.Fatal("Wait returned before Stop")
+	case <-time.After(50 * time.Millisecond):
+	}
+
+	c.Stop()
+	select {
+	case err := <-done:
+		require.NoError(t, err)
+	case <-time.After(time.Second):
+		t.Fatal("Wait did not return after Stop")
+	}
+}
+
+type fakeConn struct {
+	closed  bool
+	rebinds int
+}
+
+func (c *fakeConn) Rebind() error                             { c.rebinds++; return nil }
+func (c *fakeConn) LocalAddr() (netip.AddrPort, error)        { return netip.AddrPort{}, nil }
+func (c *fakeConn) ListenOut(_ udp.EncReader, _ func()) error { return nil }
+func (c *fakeConn) WriteTo(_ []byte, _ netip.AddrPort) error  { return nil }
+func (c *fakeConn) WriteBatch(bufs [][]byte, _ []netip.AddrPort) (int, error) {
+	return len(bufs), nil
+}
+func (c *fakeConn) ReloadConfig(_ *config.C)      {}
+func (c *fakeConn) SupportsMultipleReaders() bool { return true }
+func (c *fakeConn) Close() error                  { c.closed = true; return nil }
+
+type multiqueueDevice struct {
+	*fakeDevice
+}
+
+// Queues claims multiqueue support but fails to open the second queue,
+// exercising the activation error path.
+func (d *multiqueueDevice) Queues(n int) ([]tio.Queue, error) {
+	if n > 1 {
+		return nil, errors.New("second queue failed to open")
+	}
+	return d.fakeDevice.Queues(n)
+}
+
+func TestControl_StartMultiqueueFailureReleases(t *testing.T) {
+	dev := &multiqueueDevice{fakeDevice: newFakeDevice()}
+	conn := &fakeConn{}
+	ctx, cancel := context.WithCancel(context.Background())
+	f := &Interface{
+		ctx:      ctx,
+		inside:   dev,
+		outside:  conn,
+		writers:  []udp.Conn{conn},
+		batchers: make([]*batch.MultiCoalescer, 2),
+		routines: 2,
+		l:        test.NewLogger(),
+	}
+	f.wg.Add(1)
+
+	c := &Control{
+		state:  StateReady,
+		f:      f,
+		l:      test.NewLogger(),
+		ctx:    ctx,
+		cancel: cancel,
+	}
+
+	// The second reader fails to open, everything must be released
+	err := c.Start()
+	require.Error(t, err)
+	assert.Equal(t, StateStopped, c.State())
+	assert.True(t, dev.closed, "the tun device should have been closed")
+	assert.True(t, conn.closed, "the udp socket should have been closed")
+	require.ErrorIs(t, c.ctx.Err(), context.Canceled)
+
+	// And Wait must not hang on the construction token
+	require.NoError(t, c.Wait())
+}
+
+func TestInterface_CloseIsIdempotent(t *testing.T) {
+	dev := newFakeDevice()
+	f := &Interface{
+		inside: dev,
+		l:      test.NewLogger(),
+	}
+	f.wg.Add(1)
+
+	require.NoError(t, f.Close())
+	assert.True(t, dev.closed)
+
+	// A second Close must not double release the wg token or the device
+	require.NoError(t, f.Close())
+	require.NoError(t, f.wait())
+}
+
+func TestControl_FatalErrorReportsThroughWait(t *testing.T) {
+	c, dev, conn := newReadyControl(t)
+
+	// Mirror what Start wires up, without needing real packet readers
+	c.f.triggerShutdown = c.Stop
+	c.state = StateStarted
+
+	boom := errors.New("boom")
+	c.f.onFatal(boom)
+
+	require.ErrorIs(t, c.Wait(), boom)
+	assert.Equal(t, StateStopped, c.State())
+	assert.True(t, dev.closed)
+	assert.True(t, conn.closed)
+
+	// A second fatal error must not fire the shutdown again or replace the first
+	c.f.onFatal(errors.New("later"))
+	require.ErrorIs(t, c.Wait(), boom)
+
+	// Wait stays factual, a Stop after the death does not mask the error
+	c.Stop()
+	require.ErrorIs(t, c.Wait(), boom)
+}
+
+func TestControl_ConcurrentStopAndStart(t *testing.T) {
+	c, _, _ := newReadyControl(t)
+
+	var wg sync.WaitGroup
+	for i := 0; i < 2; i++ {
+		wg.Go(func() { c.Stop() })
+	}
+	wg.Go(func() { _ = c.Start() })
+	wg.Go(func() {
+		_ = c.Wait()
+		// A returned Wait must always observe the final state, no matter how
+		// the race resolved
+		assert.Equal(t, StateStopped, c.State())
+	})
+	wg.Wait()
+
+	// However the race resolves, the control must end fully stopped with no
+	// panic and Wait must observe the final state
+	require.NoError(t, c.Wait())
+	assert.Equal(t, StateStopped, c.State())
+	err := c.Start()
+	require.ErrorIs(t, err, ErrAlreadyStopped)
+}
+
+func TestControl_StartStopLifecycle(t *testing.T) {
+	c, dev, conn := newReadyControl(t)
+
+	err := c.Start()
+	require.NoError(t, err)
+	assert.Equal(t, StateStarted, c.State())
+	err = c.Start()
+	require.ErrorIs(t, err, ErrAlreadyStarted)
+
+	// Stop must unpark the reader blocked in the device and release everything
+	c.Stop()
+	assert.Equal(t, StateStopped, c.State())
+	assert.True(t, dev.closed, "the tun device should have been closed")
+	assert.True(t, conn.closed, "the udp socket should have been closed")
+	require.ErrorIs(t, c.ctx.Err(), context.Canceled)
+
+	// The reader drained off a closed device, that is not a fatal error
+	require.NoError(t, c.Wait())
+	err = c.Start()
+	require.ErrorIs(t, err, ErrAlreadyStopped)
+}
+
+func TestControl_RebindIsGatedByState(t *testing.T) {
+	c, _, conn := newReadyControl(t)
+
+	// A rebind before Start reaches nothing, the interface is not up
+	c.RebindUDPServer()
+	assert.Equal(t, 0, conn.rebinds, "rebind before start must be a no-op")
+
+	err := c.Start()
+	require.NoError(t, err)
+	c.RebindUDPServer()
+	assert.Equal(t, 1, conn.rebinds, "rebind while started must reach the conn")
+
+	// A rebind racing a completed stop must not touch the closed conn
+	c.Stop()
+	require.NoError(t, c.Wait())
+	c.RebindUDPServer()
+	assert.Equal(t, 1, conn.rebinds, "rebind after stop must be a no-op")
+}

control_test.go

@@ -105,7 +105,7 @@ func TestControl_GetHostInfoByVpnIp(t *testing.T) {
 	}
 
 	// Make sure we don't have any unexpected fields
-	assertFields(t, []string{"VpnAddrs", "LocalIndex", "RemoteIndex", "RemoteAddrs", "Cert", "MessageCounter", "CurrentRemote", "CurrentRelaysToMe", "CurrentRelaysThroughMe"}, thi)
+	assertFields(t, []string{"VpnAddrs", "LocalIndex", "RemoteIndex", "RemoteAddrs", "Cert", "MessageCounter", "CurrentRemote", "CurrentRelaysToMe", "CurrentRelaysThroughMe", "Lanes"}, thi)
 	assert.Equal(t, &expectedInfo, thi)
 	test.AssertDeepCopyEqual(t, &expectedInfo, thi)
 

control_tester.go

@@ -108,7 +108,29 @@ func (c *Control) GetVpnAddrs() []netip.Addr {
 }
 
 func (c *Control) GetUDPAddr() netip.AddrPort {
-	return c.f.outside.(*udp.TesterConn).Addr
+	return c.f.outside.(*udp.TesterConn).GetAddr()
+}
+
+// SetUDPAddr moves this node to a new underlay address, standing in for a laptop waking up on a different
+// network. Register the new address with the router as well or nothing will route back.
+func (c *Control) SetUDPAddr(addr netip.AddrPort) {
+	c.f.outside.(*udp.TesterConn).SetAddr(addr)
+}
+
+// SetLocalAddrsFn replaces underlay address discovery so a test can advertise its simulated address instead of
+// whatever this machine's NICs happen to be. Call it before Start, SendUpdate reads it from the update worker.
+func (c *Control) SetLocalAddrsFn(fn func(*LocalAllowList) []netip.Addr) {
+	c.f.lightHouse.localAddrsFn = fn
+}
+
+// GetRebindEpochFor returns the rebind epoch a tunnel last sent under, so a test can tell whether a send
+// consumed the epoch edge without having to infer it from lighthouse traffic.
+func (c *Control) GetRebindEpochFor(vpnAddr netip.Addr) (uint32, bool) {
+	h := c.f.hostMap.QueryVpnAddr(vpnAddr)
+	if h == nil {
+		return 0, false
+	}
+	return h.state.Load() >> stateEpochShift, true
 }
 
 func (c *Control) KillPendingTunnel(vpnIp netip.Addr) bool {
@@ -125,6 +147,14 @@ func (c *Control) GetHostmap() *HostMap {
 	return c.f.hostMap
 }
 
+// GetHostmapIndexCount returns the number of entries in the main hostmap Indexes table, holding
+// the hostmap read lock so tests can poll it while connection manager churns tunnels.
+func (c *Control) GetHostmapIndexCount() int {
+	c.f.hostMap.RLock()
+	defer c.f.hostMap.RUnlock()
+	return len(c.f.hostMap.Indexes)
+}
+
 func (c *Control) GetF() *Interface {
 	return c.f
 }

cpupick/cpupick.go

@@ -0,0 +1,187 @@
+// Package cpupick chooses which CPUs the tun reader threads pin to when the
+// operator has not chosen for us (tun.cpu_affinity). The stock spread —
+// allowed[i] for routine i — has two failure modes this package exists to fix:
+//
+//   - every co-located nebula starts its spread at allowed[0], so N instances
+//     on one box stack their readers onto the same cores, and allowed[0] is
+//     usually CPU 0, the core housekeeping and default IRQ affinity already
+//     favor;
+//   - on heterogeneous CPUs (ARM big.LITTLE, Intel P/E hybrids, AMD compact
+//     cores) low IDs are not necessarily fast cores, and pinning an encrypt
+//     thread to an efficiency core caps that queue's throughput.
+//
+// Default instead returns a preference-ordered pin list: the allowed set
+// filtered to performance cores (when the platform distinguishes them and
+// enough remain for every routine), confined to a single NUMA node and spread
+// across distinct physical cores when the topology permits, CPU 0's physical
+// core demoted to last resort, and the order rotated by a stable per-instance
+// key so co-located instances spread instead of stacking.
+package cpupick
+
+import (
+	"log/slog"
+
+	"github.com/slackhq/nebula/util"
+)
+
+// topology is the slice of machine layout arrange consults: the NUMA node
+// and the physical core behind each candidate CPU, plus which core CPU 0
+// lives on (zeroCore, -1 when unknown — tracked separately because CPU 0's
+// SMT sibling deserves demotion even when CPU 0 itself isn't a candidate).
+// Probed from sysfs on Linux; flatTopology stands in when the platform can't
+// say, which turns every topology rule into a no-op rather than a wrong
+// answer.
+type topology struct {
+	nodeOf   map[int]int
+	coreOf   map[int]int
+	zeroCore int
+}
+
+// flatTopology places every CPU on node 0 and on a physical core of its own.
+func flatTopology(cpus []int) topology {
+	t := topology{
+		nodeOf:   make(map[int]int, len(cpus)),
+		coreOf:   make(map[int]int, len(cpus)),
+		zeroCore: -1,
+	}
+	for i, c := range cpus {
+		t.nodeOf[c] = 0
+		t.coreOf[c] = i
+		if c == 0 {
+			t.zeroCore = i
+		}
+	}
+	return t
+}
+
+// Default computes the pin order for `routines` tun readers. key is any
+// stable per-instance value; the bound UDP port is ideal — distinct across
+// co-located instances, stable across restarts so benchmark runs stay
+// comparable. Returns nil when there is nothing useful to say (no affinity
+// support on this platform, lookup failure); callers keep their existing
+// fallback spread.
+func Default(routines int, key uint64, l *slog.Logger) []int {
+	allowed, err := util.AllowedCPUs()
+	if err != nil || len(allowed) == 0 {
+		return nil
+	}
+	perf, signal := perfCPUs(allowed)
+	cands := pickCandidates(allowed, perf, routines)
+	if len(cands) == 0 {
+		return nil
+	}
+	if len(perf) < routines {
+		signal = ""
+	}
+	cpus := arrange(cands, readTopology(cands), routines, splitmix64(key))
+	if l != nil {
+		l.Info("chose default pin CPUs for tun readers",
+			"cpus", cpus[:min(routines, len(cpus))],
+			"perfSignal", signal)
+	}
+	return cpus
+}
+
+// pickCandidates applies the enough-for-everyone guard: a perf filter that
+// leaves fewer candidates than routines is discarded — giving every reader
+// its own (possibly slow) core beats stacking two readers on a fast one.
+func pickCandidates(allowed, perf []int, routines int) []int {
+	if len(perf) < routines {
+		return allowed
+	}
+	return perf
+}
+
+// arrange turns the candidate set into the final pin order:
+//
+//  1. NUMA: when at least one node holds enough candidates for every
+//     routine, confine to one such node, chosen by the instance hash. The
+//     readers share hostmap and cipher state, so splitting one instance
+//     across nodes taxes every packet — and co-located instances that hash
+//     to different nodes stop competing entirely. When no node is big
+//     enough, span nodes rather than stack readers.
+//  2. Rotate the preferred candidates by the hash so instances spread.
+//  3. SMT: emit one thread per physical core before any of their siblings —
+//     two encrypt threads on one core split its execution units. Siblings
+//     still follow for the routines > cores case.
+//  4. CPU 0's whole physical core goes last: housekeeping and default IRQ
+//     noise on CPU 0 bleeds into its SMT sibling too. Within that tail the
+//     sibling precedes CPU 0 itself, which only catches the bleed-through.
+//
+// The rotation happens before the SMT pass so each instance's one-per-core
+// walk also starts at a different core, and CPU 0's core is excluded from
+// the rotation so no hash value can put it back at the front.
+func arrange(cands []int, topo topology, routines int, h uint64) []int {
+	byNode := map[int][]int{}
+	var nodes []int
+	for _, c := range cands {
+		n := topo.nodeOf[c]
+		if _, ok := byNode[n]; !ok {
+			nodes = append(nodes, n)
+		}
+		byNode[n] = append(byNode[n], c)
+	}
+	var eligible []int
+	for _, n := range nodes {
+		if len(byNode[n]) >= routines {
+			eligible = append(eligible, n)
+		}
+	}
+	if len(eligible) > 0 {
+		cands = byNode[eligible[int(h%uint64(len(eligible)))]]
+	}
+
+	// Split off CPU 0's core: its siblings tail the list, CPU 0 tails them.
+	preferred := make([]int, 0, len(cands))
+	var zeroTail []int
+	hasZero := false
+	for _, c := range cands {
+		switch {
+		case c == 0:
+			hasZero = true
+		case topo.zeroCore >= 0 && topo.coreOf[c] == topo.zeroCore:
+			zeroTail = append(zeroTail, c)
+		default:
+			preferred = append(preferred, c)
+		}
+	}
+	if hasZero {
+		zeroTail = append(zeroTail, 0)
+	}
+	if len(preferred) == 0 {
+		return zeroTail // CPU 0's core is all we have
+	}
+
+	// The node pick consumed the low hash bits; rotate by the high ones so
+	// the two choices stay independent.
+	off := int((h >> 32) % uint64(len(preferred)))
+	rot := make([]int, 0, len(preferred))
+	rot = append(rot, preferred[off:]...)
+	rot = append(rot, preferred[:off]...)
+
+	seenCore := make(map[int]bool, len(rot))
+	out := make([]int, 0, len(cands))
+	var siblings []int
+	for _, c := range rot {
+		g := topo.coreOf[c]
+		if seenCore[g] {
+			siblings = append(siblings, c)
+			continue
+		}
+		seenCore[g] = true
+		out = append(out, c)
+	}
+	out = append(out, siblings...)
+	out = append(out, zeroTail...)
+	return out
+}
+
+// splitmix64 decorrelates instance keys before the selection modulos: ports
+// on one box often share spacing (4242/4243, or round steps like +1000) that
+// raw key%len arithmetic would fold onto the same offset.
+func splitmix64(x uint64) uint64 {
+	x += 0x9e3779b97f4a7c15
+	x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9
+	x = (x ^ (x >> 27)) * 0x94d049bb133111eb
+	return x ^ (x >> 31)
+}

cpupick/cpupick_test.go

@@ -0,0 +1,171 @@
+package cpupick
+
+import (
+	"slices"
+	"testing"
+)
+
+// pairTopo builds a topology where consecutive candidate pairs are SMT
+// siblings: (cpus[0],cpus[1]) share a core, (cpus[2],cpus[3]) the next, ...
+// All CPUs land on node 0.
+func pairTopo(cpus []int) topology {
+	t := topology{
+		nodeOf:   make(map[int]int, len(cpus)),
+		coreOf:   make(map[int]int, len(cpus)),
+		zeroCore: -1,
+	}
+	for i, c := range cpus {
+		t.nodeOf[c] = 0
+		t.coreOf[c] = i / 2
+		if c == 0 {
+			t.zeroCore = i / 2
+		}
+	}
+	return t
+}
+
+func TestArrangeDemotesZeroForEveryKey(t *testing.T) {
+	candidates := []int{0, 1, 2, 3, 4, 5, 6, 7}
+	for key := range uint64(64) {
+		got := arrange(candidates, flatTopology(candidates), 4, splitmix64(key))
+		if len(got) != len(candidates) {
+			t.Fatalf("key %d: len=%d want %d", key, len(got), len(candidates))
+		}
+		if got[0] == 0 {
+			t.Errorf("key %d: CPU 0 at the front: %v", key, got)
+		}
+		if got[len(got)-1] != 0 {
+			t.Errorf("key %d: CPU 0 not demoted to last: %v", key, got)
+		}
+		sorted := slices.Clone(got)
+		slices.Sort(sorted)
+		if !slices.Equal(sorted, candidates) {
+			t.Errorf("key %d: not a permutation: %v", key, got)
+		}
+	}
+}
+
+func TestArrangeDemotesZeroSiblings(t *testing.T) {
+	// Pairs (0,1),(2,3),(4,5),(6,7): CPU 0's core — 0 and its sibling 1 —
+	// must tail the list, sibling ahead of 0 itself.
+	candidates := []int{0, 1, 2, 3, 4, 5, 6, 7}
+	for key := range uint64(64) {
+		got := arrange(candidates, pairTopo(candidates), 2, splitmix64(key))
+		n := len(got)
+		if got[n-1] != 0 || got[n-2] != 1 {
+			t.Fatalf("key %d: tail = %v, want [... 1 0]", key, got)
+		}
+	}
+}
+
+func TestArrangeZeroSiblingWithoutZero(t *testing.T) {
+	// CPU 0 excluded (cpuset) but its sibling 1 remains: the sibling still
+	// tails the list when the topology knows which core CPU 0 lives on.
+	candidates := []int{1, 2, 3, 4, 5}
+	topo := pairTopo([]int{0, 1, 2, 3, 4, 5})
+	got := arrange(candidates, topo, 2, splitmix64(7))
+	if got[len(got)-1] != 1 {
+		t.Errorf("CPU 0's sibling not demoted: %v", got)
+	}
+}
+
+func TestArrangeRotatesByKey(t *testing.T) {
+	candidates := []int{1, 2, 3, 4, 5, 6, 7, 8}
+	seen := map[int]bool{}
+	for key := range uint64(64) {
+		seen[arrange(candidates, flatTopology(candidates), 4, splitmix64(key))[0]] = true
+	}
+	// 64 hashed keys over 8 slots must hit more than one starting CPU, or
+	// co-located instances would all stack again.
+	if len(seen) < 2 {
+		t.Errorf("rotation never varied across keys: %v", seen)
+	}
+}
+
+func TestArrangeStableForSameKey(t *testing.T) {
+	candidates := []int{0, 2, 4, 6}
+	topo := flatTopology(candidates)
+	a := arrange(candidates, topo, 2, splitmix64(4242))
+	b := arrange(candidates, topo, 2, splitmix64(4242))
+	if !slices.Equal(a, b) {
+		t.Errorf("same key ordered differently: %v vs %v", a, b)
+	}
+}
+
+func TestArrangeZeroOnly(t *testing.T) {
+	if got := arrange([]int{0}, flatTopology([]int{0}), 1, splitmix64(7)); !slices.Equal(got, []int{0}) {
+		t.Errorf("sole CPU 0 must survive: %v", got)
+	}
+}
+
+func TestArrangeSMTSiblingsLast(t *testing.T) {
+	// Pairs (1,2),(3,4),(5,6),(7,8): the first four picks must cover four
+	// distinct physical cores before any sibling repeats.
+	candidates := []int{1, 2, 3, 4, 5, 6, 7, 8}
+	topo := pairTopo(candidates)
+	for key := range uint64(16) {
+		got := arrange(candidates, topo, 4, splitmix64(key))
+		seen := map[int]bool{}
+		for _, c := range got[:4] {
+			g := topo.coreOf[c]
+			if seen[g] {
+				t.Fatalf("key %d: sibling before all cores covered: %v", key, got)
+			}
+			seen[g] = true
+		}
+	}
+}
+
+func TestArrangeNUMAConfinesToOneNode(t *testing.T) {
+	// Two nodes of four; both fit routines=3, so the result must sit
+	// entirely inside one of them, and the hash must pick both across keys.
+	candidates := []int{1, 2, 3, 4, 10, 11, 12, 13}
+	topo := flatTopology(candidates)
+	for _, c := range []int{10, 11, 12, 13} {
+		topo.nodeOf[c] = 1
+	}
+	nodesSeen := map[int]bool{}
+	for key := range uint64(32) {
+		got := arrange(candidates, topo, 3, splitmix64(key))
+		if len(got) != 4 {
+			t.Fatalf("key %d: not confined to one node: %v", key, got)
+		}
+		n := topo.nodeOf[got[0]]
+		for _, c := range got {
+			if topo.nodeOf[c] != n {
+				t.Fatalf("key %d: spans nodes: %v", key, got)
+			}
+		}
+		nodesSeen[n] = true
+	}
+	if len(nodesSeen) != 2 {
+		t.Errorf("hash never spread instances across nodes: %v", nodesSeen)
+	}
+}
+
+func TestArrangeNUMASpansWhenNoNodeFits(t *testing.T) {
+	candidates := []int{1, 2, 3, 4, 10, 11, 12, 13}
+	topo := flatTopology(candidates)
+	for _, c := range []int{10, 11, 12, 13} {
+		topo.nodeOf[c] = 1
+	}
+	got := arrange(candidates, topo, 6, splitmix64(1))
+	if len(got) != len(candidates) {
+		t.Errorf("undersized nodes must span, got %v", got)
+	}
+}
+
+func TestPickCandidates(t *testing.T) {
+	allowed := []int{0, 1, 2, 3, 4, 5, 6, 7}
+	perf := []int{4, 5}
+
+	// Enough perf cores for every routine: only they are used.
+	if got := pickCandidates(allowed, perf, 2); !slices.Equal(got, perf) {
+		t.Errorf("perf filter not applied: %v", got)
+	}
+	// Perf filter too small for the routine count: discarded, everyone
+	// gets their own core from the full allowed set.
+	if got := pickCandidates(allowed, perf, 4); !slices.Equal(got, allowed) {
+		t.Errorf("undersized perf filter not discarded: %v", got)
+	}
+}

cpupick/perf_linux.go

@@ -0,0 +1,154 @@
+//go:build linux
+
+package cpupick
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// capacityKeepPct is the cpu_capacity admission threshold, relative to the
+// fastest allowed core. LITTLE cores are normalized to ~250-400 of the big
+// core's 1024 while mid cores sit at ~75%+, so half of max separates little
+// from the rest without splitting prime from mid on three-tier parts.
+const capacityKeepPct = 50
+
+// freqKeepPct is the cpuinfo_max_freq admission threshold. Favored-core
+// turbo skew is 2-4% and ARM mid-vs-prime ~12%, while E-cores, LITTLE
+// cores, and AMD compact cores all sit >= 20% below their siblings' max.
+const freqKeepPct = 85
+
+// perfCPUs partitions allowed into the subset that are "performance" cores,
+// consulting (in order of authority):
+//
+//  1. cpu_capacity — arch_topology's normalized per-CPU capacity, exposed on
+//     arm/arm64/riscv; the scheduler's own view of big vs LITTLE.
+//  2. /sys/devices/cpu_core/cpus — the Intel hybrid P-core PMU mask, present
+//     only on P/E parts (x86 has no cpu_capacity) and naming P cores outright.
+//  3. cpuinfo_max_freq — the cross-vendor fallback; catches AMD compact
+//     cores, which neither of the above covers.
+//
+// Returns allowed unchanged (signal "") when nothing distinguishes the
+// cores: homogeneous parts, VMs without cpufreq, sysfs unavailable.
+func perfCPUs(allowed []int) ([]int, string) {
+	return perfCPUsFrom("/sys/devices/system/cpu", "/sys/devices/cpu_core/cpus", allowed)
+}
+
+func perfCPUsFrom(cpuDir, intelCoreMask string, allowed []int) ([]int, string) {
+	if cpus, ok := byPerCPUValue(cpuDir, "cpu_capacity", allowed, capacityKeepPct); ok {
+		return cpus, "cpu_capacity"
+	}
+	if cpus, ok := byIntelCoreMask(intelCoreMask, allowed); ok {
+		return cpus, "intel_core_pmu"
+	}
+	if cpus, ok := byPerCPUValue(cpuDir, "cpufreq/cpuinfo_max_freq", allowed, freqKeepPct); ok {
+		return cpus, "max_freq"
+	}
+	return allowed, ""
+}
+
+// byPerCPUValue keeps the allowed CPUs whose per-CPU sysfs value is at least
+// keepPct percent of the maximum across allowed. Inconclusive (ok=false)
+// when any CPU is missing the file or when every value is equal.
+func byPerCPUValue(cpuDir, file string, allowed []int, keepPct int) ([]int, bool) {
+	vals := make([]int, len(allowed))
+	minV, maxV := 0, 0
+	for i, cpu := range allowed {
+		v, err := readIntFile(filepath.Join(cpuDir, fmt.Sprintf("cpu%d", cpu), file))
+		if err != nil {
+			return nil, false
+		}
+		vals[i] = v
+		if i == 0 || v < minV {
+			minV = v
+		}
+		if v > maxV {
+			maxV = v
+		}
+	}
+	if minV == maxV {
+		return nil, false // homogeneous by this signal; try the next one
+	}
+	keep := make([]int, 0, len(allowed))
+	for i, cpu := range allowed {
+		if vals[i]*100 >= maxV*keepPct {
+			keep = append(keep, cpu)
+		}
+	}
+	return keep, true
+}
+
+// byIntelCoreMask keeps the allowed CPUs named by the hybrid P-core PMU
+// mask. Inconclusive when the file is absent (non-hybrid x86, other arches)
+// or no allowed CPU is in the mask (the process was deliberately confined
+// to E-cores; nothing useful to prefer within that).
+func byIntelCoreMask(maskPath string, allowed []int) ([]int, bool) {
+	b, err := os.ReadFile(maskPath)
+	if err != nil {
+		return nil, false
+	}
+	set, err := parseCPUList(strings.TrimSpace(string(b)))
+	if err != nil || len(set) == 0 {
+		return nil, false
+	}
+	pcore := make(map[int]bool, len(set))
+	for _, c := range set {
+		pcore[c] = true
+	}
+	keep := make([]int, 0, len(allowed))
+	for _, cpu := range allowed {
+		if pcore[cpu] {
+			keep = append(keep, cpu)
+		}
+	}
+	if len(keep) == 0 {
+		return nil, false
+	}
+	return keep, true
+}
+
+// parseCPUList decodes the kernel's cpulist format ("0-7,16-23", "3") into
+// individual CPU IDs. Empty input yields an empty list.
+func parseCPUList(s string) ([]int, error) {
+	if s == "" {
+		return nil, nil
+	}
+	var out []int
+	for part := range strings.SplitSeq(s, ",") {
+		part = strings.TrimSpace(part)
+		if part == "" {
+			continue
+		}
+		lo, hi, isRange := strings.Cut(part, "-")
+		a, err := strconv.Atoi(lo)
+		if err != nil {
+			return nil, fmt.Errorf("bad cpulist entry %q: %w", part, err)
+		}
+		if !isRange {
+			out = append(out, a)
+			continue
+		}
+		b, err := strconv.Atoi(hi)
+		if err != nil {
+			return nil, fmt.Errorf("bad cpulist entry %q: %w", part, err)
+		}
+		if b < a || b-a > 8192 {
+			return nil, fmt.Errorf("bad cpulist range %q", part)
+		}
+		for v := a; v <= b; v++ {
+			out = append(out, v)
+		}
+	}
+	return out, nil
+}
+
+func readIntFile(path string) (int, error) {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.Atoi(strings.TrimSpace(string(b)))
+}

cpupick/perf_linux_test.go

@@ -0,0 +1,163 @@
+//go:build linux
+
+package cpupick
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"testing"
+)
+
+// fakeSysfs builds a cpuDir tree with the given per-CPU file values.
+// A nil map for a file means "file absent on every CPU".
+func fakeSysfs(t *testing.T, capacity, maxFreq map[int]int) string {
+	t.Helper()
+	dir := t.TempDir()
+	write := func(cpu int, rel string, v int) {
+		p := filepath.Join(dir, fmt.Sprintf("cpu%d", cpu), rel)
+		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(p, fmt.Appendf(nil, "%d\n", v), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for cpu, v := range capacity {
+		write(cpu, "cpu_capacity", v)
+	}
+	for cpu, v := range maxFreq {
+		write(cpu, "cpufreq/cpuinfo_max_freq", v)
+	}
+	return dir
+}
+
+func writeCoreMask(t *testing.T, mask string) string {
+	t.Helper()
+	p := filepath.Join(t.TempDir(), "cpus")
+	if err := os.WriteFile(p, []byte(mask+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	return p
+}
+
+func TestPerfCPUsBigLittleCapacity(t *testing.T) {
+	// 4 big (1024) + 4 LITTLE (~290): capacity is authoritative on ARM.
+	dir := fakeSysfs(t, map[int]int{
+		0: 1024, 1: 1024, 2: 1024, 3: 1024,
+		4: 290, 5: 290, 6: 290, 7: 290,
+	}, nil)
+	got, signal := perfCPUsFrom(dir, filepath.Join(dir, "nope"), []int{0, 1, 2, 3, 4, 5, 6, 7})
+	if signal != "cpu_capacity" {
+		t.Fatalf("signal = %q", signal)
+	}
+	if !slices.Equal(got, []int{0, 1, 2, 3}) {
+		t.Errorf("got %v", got)
+	}
+}
+
+func TestPerfCPUsThreeTierKeepsMid(t *testing.T) {
+	// prime (1024) + mid (~780) + little (~280): 50% keeps prime+mid.
+	dir := fakeSysfs(t, map[int]int{
+		0: 280, 1: 280, 2: 280, 3: 280,
+		4: 780, 5: 780, 6: 780,
+		7: 1024,
+	}, nil)
+	got, _ := perfCPUsFrom(dir, filepath.Join(dir, "nope"), []int{0, 1, 2, 3, 4, 5, 6, 7})
+	if !slices.Equal(got, []int{4, 5, 6, 7}) {
+		t.Errorf("got %v", got)
+	}
+}
+
+func TestPerfCPUsIntelHybridMask(t *testing.T) {
+	// No cpu_capacity on x86; the P-core PMU mask decides.
+	dir := fakeSysfs(t, nil, nil)
+	mask := writeCoreMask(t, "0-7")
+	got, signal := perfCPUsFrom(dir, mask, []int{0, 1, 2, 3, 8, 9, 10, 11})
+	if signal != "intel_core_pmu" {
+		t.Fatalf("signal = %q", signal)
+	}
+	if !slices.Equal(got, []int{0, 1, 2, 3}) {
+		t.Errorf("got %v", got)
+	}
+}
+
+func TestPerfCPUsIntelMaskDisjointFallsThrough(t *testing.T) {
+	// Confined to E-cores only: the mask can't help, and equal freqs below
+	// mean nothing else distinguishes them either -> allowed unchanged.
+	dir := fakeSysfs(t, nil, map[int]int{8: 4300000, 9: 4300000})
+	mask := writeCoreMask(t, "0-7")
+	got, signal := perfCPUsFrom(dir, mask, []int{8, 9})
+	if signal != "" || !slices.Equal(got, []int{8, 9}) {
+		t.Errorf("got %v signal %q", got, signal)
+	}
+}
+
+func TestPerfCPUsMaxFreqCompactCores(t *testing.T) {
+	// AMD-style compact cores: no capacity, no Intel mask; 3.3 vs 5.7 GHz.
+	dir := fakeSysfs(t, nil, map[int]int{
+		0: 5700000, 1: 5700000, 2: 3300000, 3: 3300000,
+	})
+	got, signal := perfCPUsFrom(dir, filepath.Join(dir, "nope"), []int{0, 1, 2, 3})
+	if signal != "max_freq" {
+		t.Fatalf("signal = %q", signal)
+	}
+	if !slices.Equal(got, []int{0, 1}) {
+		t.Errorf("got %v", got)
+	}
+}
+
+func TestPerfCPUsFavoredCoreSkewKept(t *testing.T) {
+	// Turbo Boost Max favored cores run a few percent hot; they must not
+	// shrink the candidate set to one or two cores.
+	dir := fakeSysfs(t, nil, map[int]int{
+		0: 5800000, 1: 5700000, 2: 5700000, 3: 5600000,
+	})
+	got, _ := perfCPUsFrom(dir, filepath.Join(dir, "nope"), []int{0, 1, 2, 3})
+	if !slices.Equal(got, []int{0, 1, 2, 3}) {
+		t.Errorf("favored-core skew filtered CPUs: %v", got)
+	}
+}
+
+func TestPerfCPUsHomogeneousInconclusive(t *testing.T) {
+	dir := fakeSysfs(t, nil, map[int]int{0: 3000000, 1: 3000000})
+	got, signal := perfCPUsFrom(dir, filepath.Join(dir, "nope"), []int{0, 1})
+	if signal != "" || !slices.Equal(got, []int{0, 1}) {
+		t.Errorf("got %v signal %q", got, signal)
+	}
+}
+
+func TestPerfCPUsNoSysfs(t *testing.T) {
+	dir := t.TempDir()
+	got, signal := perfCPUsFrom(dir, filepath.Join(dir, "nope"), []int{0, 1, 2})
+	if signal != "" || !slices.Equal(got, []int{0, 1, 2}) {
+		t.Errorf("got %v signal %q", got, signal)
+	}
+}
+
+func TestParseCPUList(t *testing.T) {
+	cases := []struct {
+		in      string
+		want    []int
+		wantErr bool
+	}{
+		{"0-3", []int{0, 1, 2, 3}, false},
+		{"0-1,16-17", []int{0, 1, 16, 17}, false},
+		{"5", []int{5}, false},
+		{"", nil, false},
+		{"3-1", nil, true},
+		{"a-b", nil, true},
+		{"1,x", nil, true},
+	}
+	for _, c := range cases {
+		got, err := parseCPUList(c.in)
+		if (err != nil) != c.wantErr {
+			t.Errorf("%q: err=%v wantErr=%v", c.in, err, c.wantErr)
+			continue
+		}
+		if !c.wantErr && !slices.Equal(got, c.want) {
+			t.Errorf("%q: got %v want %v", c.in, got, c.want)
+		}
+	}
+}

cpupick/perf_other.go

@@ -0,0 +1,10 @@
+//go:build !linux
+
+package cpupick
+
+// perfCPUs is Linux-only sysfs walking; elsewhere report "no distinction".
+// Default already returns nil off-Linux (util.AllowedCPUs has no answer
+// there), so this exists to keep the package compiling everywhere.
+func perfCPUs(allowed []int) ([]int, string) {
+	return allowed, ""
+}

cpupick/topo_linux.go

@@ -0,0 +1,118 @@
+//go:build linux
+
+package cpupick
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// readTopology probes the NUMA node and physical-core layout of cpus from
+// sysfs. Anything sysfs won't say degrades toward flatTopology: an unknown
+// node becomes node 0, an unknown core becomes a core of its own — either
+// way the corresponding arrange rule becomes a no-op instead of a wrong
+// answer.
+func readTopology(cpus []int) topology {
+	return readTopologyFrom("/sys/devices/system/node", "/sys/devices/system/cpu", cpus)
+}
+
+func readTopologyFrom(nodeDir, cpuDir string, cpus []int) topology {
+	coreOf, zeroCore := coreGroups(cpuDir, cpus)
+	return topology{
+		nodeOf:   numaNodes(nodeDir, cpus),
+		coreOf:   coreOf,
+		zeroCore: zeroCore,
+	}
+}
+
+// numaNodes maps each cpu to its NUMA node via
+// /sys/devices/system/node/nodeN/cpulist. CPUs no node claims (or no node
+// dirs at all: VMs, non-NUMA kernels) land on node 0.
+func numaNodes(nodeDir string, cpus []int) map[int]int {
+	out := make(map[int]int, len(cpus))
+	for _, c := range cpus {
+		out[c] = 0
+	}
+	entries, err := os.ReadDir(nodeDir)
+	if err != nil {
+		return out
+	}
+	want := make(map[int]bool, len(cpus))
+	for _, c := range cpus {
+		want[c] = true
+	}
+	for _, e := range entries {
+		id, ok := strings.CutPrefix(e.Name(), "node")
+		if !ok {
+			continue
+		}
+		n, err := strconv.Atoi(id)
+		if err != nil {
+			continue // has_cpu, possible, ... share the prefix
+		}
+		b, err := os.ReadFile(filepath.Join(nodeDir, e.Name(), "cpulist"))
+		if err != nil {
+			continue
+		}
+		list, err := parseCPUList(strings.TrimSpace(string(b)))
+		if err != nil {
+			continue
+		}
+		for _, c := range list {
+			if want[c] {
+				out[c] = n
+			}
+		}
+	}
+	return out
+}
+
+// coreGroups maps each cpu to a dense physical-core id derived from its
+// (physical_package_id, core_id) pair — core_id alone repeats across
+// sockets. CPUs whose topology files are unreadable get a core of their own.
+// The second return is the group id of the core CPU 0 lives on, or -1 when
+// that can't be determined; CPU 0's own files are consulted even when 0 is
+// not a candidate, so its SMT siblings are recognized under cpusets that
+// exclude CPU 0 itself.
+func coreGroups(cpuDir string, cpus []int) (map[int]int, int) {
+	type pkgCore struct{ pkg, core int }
+	pairOf := func(cpu int) (pkgCore, bool) {
+		topoDir := filepath.Join(cpuDir, fmt.Sprintf("cpu%d", cpu), "topology")
+		pkg, err1 := readIntFile(filepath.Join(topoDir, "physical_package_id"))
+		core, err2 := readIntFile(filepath.Join(topoDir, "core_id"))
+		if err1 != nil || err2 != nil {
+			return pkgCore{}, false
+		}
+		return pkgCore{pkg, core}, true
+	}
+
+	ids := map[pkgCore]int{}
+	out := make(map[int]int, len(cpus))
+	next := 0
+	for _, cpu := range cpus {
+		k, ok := pairOf(cpu)
+		if !ok {
+			out[cpu] = next
+			next++
+			continue
+		}
+		id, ok := ids[k]
+		if !ok {
+			id = next
+			next++
+			ids[k] = id
+		}
+		out[cpu] = id
+	}
+
+	zeroCore := -1
+	if k, ok := pairOf(0); ok {
+		if id, ok := ids[k]; ok {
+			zeroCore = id
+		}
+	}
+	return out, zeroCore
+}

cpupick/topo_linux_test.go

@@ -0,0 +1,111 @@
+//go:build linux
+
+package cpupick
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// fakeTopoSysfs builds nodeDir/cpuDir trees. nodes maps node id -> cpulist
+// string; cores maps cpu -> (package, core) pair.
+func fakeTopoSysfs(t *testing.T, nodes map[int]string, cores map[int][2]int) (string, string) {
+	t.Helper()
+	base := t.TempDir()
+	nodeDir := filepath.Join(base, "node")
+	cpuDir := filepath.Join(base, "cpu")
+	for n, list := range nodes {
+		d := filepath.Join(nodeDir, fmt.Sprintf("node%d", n))
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(d, "cpulist"), []byte(list+"\n"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for cpu, pc := range cores {
+		d := filepath.Join(cpuDir, fmt.Sprintf("cpu%d", cpu), "topology")
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(d, "physical_package_id"), fmt.Appendf(nil, "%d\n", pc[0]), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(d, "core_id"), fmt.Appendf(nil, "%d\n", pc[1]), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return nodeDir, cpuDir
+}
+
+func TestReadTopology(t *testing.T) {
+	// Two nodes; SMT pairs (0,4),(1,5) on node 0 and (2,6),(3,7) on node 1.
+	// core_id repeats across packages on purpose: the pair must disambiguate.
+	nodeDir, cpuDir := fakeTopoSysfs(t,
+		map[int]string{0: "0-1,4-5", 1: "2-3,6-7"},
+		map[int][2]int{
+			0: {0, 0}, 4: {0, 0}, 1: {0, 1}, 5: {0, 1},
+			2: {1, 0}, 6: {1, 0}, 3: {1, 1}, 7: {1, 1},
+		})
+	cpus := []int{0, 1, 2, 3, 4, 5, 6, 7}
+	topo := readTopologyFrom(nodeDir, cpuDir, cpus)
+
+	for _, c := range []int{0, 1, 4, 5} {
+		if topo.nodeOf[c] != 0 {
+			t.Errorf("cpu %d on node %d, want 0", c, topo.nodeOf[c])
+		}
+	}
+	for _, c := range []int{2, 3, 6, 7} {
+		if topo.nodeOf[c] != 1 {
+			t.Errorf("cpu %d on node %d, want 1", c, topo.nodeOf[c])
+		}
+	}
+	pairs := [][2]int{{0, 4}, {1, 5}, {2, 6}, {3, 7}}
+	for _, p := range pairs {
+		if topo.coreOf[p[0]] != topo.coreOf[p[1]] {
+			t.Errorf("siblings %v not grouped: %d vs %d", p, topo.coreOf[p[0]], topo.coreOf[p[1]])
+		}
+	}
+	if topo.coreOf[0] == topo.coreOf[2] {
+		t.Error("cross-package cores with equal core_id must not merge")
+	}
+	if topo.zeroCore != topo.coreOf[0] {
+		t.Errorf("zeroCore = %d, want %d", topo.zeroCore, topo.coreOf[0])
+	}
+}
+
+func TestReadTopologyZeroCoreWithoutZeroCandidate(t *testing.T) {
+	// CPU 0 is not a candidate (cpuset excludes it) but its sibling 4 is:
+	// zeroCore must still identify their shared core.
+	nodeDir, cpuDir := fakeTopoSysfs(t,
+		map[int]string{0: "0-7"},
+		map[int][2]int{0: {0, 0}, 4: {0, 0}, 1: {0, 1}, 5: {0, 1}})
+	topo := readTopologyFrom(nodeDir, cpuDir, []int{1, 4, 5})
+	if topo.zeroCore < 0 || topo.coreOf[4] != topo.zeroCore {
+		t.Errorf("zeroCore = %d, coreOf[4] = %d; sibling of CPU 0 not identified", topo.zeroCore, topo.coreOf[4])
+	}
+	if topo.coreOf[1] == topo.zeroCore {
+		t.Error("cpu 1 wrongly grouped with CPU 0's core")
+	}
+}
+
+func TestReadTopologyMissingSysfs(t *testing.T) {
+	base := t.TempDir()
+	cpus := []int{0, 1, 2}
+	topo := readTopologyFrom(filepath.Join(base, "nope"), filepath.Join(base, "also-nope"), cpus)
+	seen := map[int]bool{}
+	for _, c := range cpus {
+		if topo.nodeOf[c] != 0 {
+			t.Errorf("cpu %d node = %d, want 0", c, topo.nodeOf[c])
+		}
+		if seen[topo.coreOf[c]] {
+			t.Errorf("cpu %d shares a fallback core group", c)
+		}
+		seen[topo.coreOf[c]] = true
+	}
+	if topo.zeroCore != -1 {
+		t.Errorf("zeroCore = %d, want -1 when unknown", topo.zeroCore)
+	}
+}

cpupick/topo_other.go

@@ -0,0 +1,10 @@
+//go:build !linux
+
+package cpupick
+
+// readTopology has no sysfs to consult off Linux; the flat stand-in makes
+// arrange's NUMA and SMT rules no-ops. Default is already nil off Linux
+// (util.AllowedCPUs has no answer there) — this keeps the package compiling.
+func readTopology(cpus []int) topology {
+	return flatTopology(cpus)
+}

design/multiport.md

@@ -0,0 +1,526 @@
+# Multiport lanes
+
+Status: experimental. Linux only. Off unless `multiport.ports` is set.
+
+## The problem
+
+A nebula tunnel is one UDP 4-tuple. Everything between the two hosts that makes
+a decision per flow makes it once, for the whole tunnel:
+
+- **ECMP / LAG** hashes the 4-tuple and picks one path. A tunnel gets one path's
+  worth of bandwidth no matter how many exist.
+- **NIC RSS** hashes the 4-tuple to one receive queue, so one CPU takes every
+  interrupt for the tunnel and receive is capped by a single core.
+- **Per-flow policers and shapers** see one flow and rate-limit it as one.
+- **Cloud per-flow bandwidth caps** are the hard version of that. AWS EC2 meters
+  each 5-tuple separately and caps a single flow well below what the instance can
+  do in aggregate -- on the order of 5 Gbps for a single flow within a VPC (more
+  inside a cluster placement group, or with ENA Express; check the current EC2
+  network-limits docs for exact numbers) on instances whose aggregate allowance
+  is many times that. Other providers do the same. Nothing about the path is
+  saturated when this fires, and no amount of retuning changes it: the hypervisor
+  is metering *the flow*, so the only way to get more is to be more than one
+  flow.
+
+Running `routines: N` does not help. Those N sockets share one port through
+`SO_REUSEPORT`, and the group is keyed on the exact `(addr, port)` pair, so the
+kernel's reuseport hash is the *only* thing spreading the work -- every hash
+outside this host still sees a single flow.
+
+Multiport gives one tunnel several underlay 4-tuples, so all of those per-flow
+decisions get made several times, independently. A tunnel with N lanes is N
+flows to everything counting flows: N ECMP hashes, N receive queues, N of the
+cloud provider's per-flow buckets.
+
+There is a second bottleneck, and it is inside this host rather than out on the
+network: in FIPS 140 mode the AES-GCM implementation refuses to seal twice under
+the same nonce, which forces every encrypt on a session to be serialized behind
+one mutex. `routines: N` does not help there either. Because each lane is a
+separate session, multiport splits that mutex as well -- see
+[The FIPS 140 encrypt lock](#the-fips-140-encrypt-lock).
+
+## What a lane is
+
+A lane is **not** a second tunnel. It is an extra session on the same
+`HostInfo`.
+
+Noise leaves both sides with `A.eKey == B.dKey` and `A.dKey == B.eKey`. Expanding
+both keys through HKDF-SHA256 with the same per-lane label preserves that
+equality, so both sides land on a matched key pair having exchanged nothing:
+
+```
+lane s send key = HKDF(base eKey, info: "nebula multiport lane v1 <s>")
+lane s recv key = HKDF(base dKey, info: "nebula multiport lane v1 <s>")
+```
+
+(`connection_state.go:deriveLaneKey`. The base key is already unique per tunnel
+and per direction, so the lane index is the only thing that needs to vary and no
+salt is required.)
+
+Consequences worth stating plainly:
+
+- A lane costs **no handshake** and has no half-established state.
+- A lane dies exactly when its base tunnel dies. There is no independent
+  lifetime to reason about, no second teardown path.
+- Each lane is a **full** session: its own message counter, its own replay
+  window, its own cipher states, its own encrypt lock. Flows on different paths
+  never contend for shared replay state, which is what makes reordering across
+  lanes harmless, and under FIPS 140 the separate encrypt locks are what let one
+  tunnel encrypt on more than one core.
+- Rolling the base tunnel replaces every lane key, because lanes are derived
+  from it. `maxMessageCounter` therefore reports the max across the base and all
+  lane counters, so rehandshake and exhaustion thresholds see the real data
+  volume rather than the base session's small share.
+
+Which lane a packet belongs to travels in the nebula header, in the low 8 bits
+of what used to be `Reserved` (see `header/header.go`). It is part of the AEAD's
+associated data, so a lane index cannot be altered in flight -- a packet
+decrypts on the lane it claims or not at all.
+
+**Lane 0 is the base tunnel itself**: `HostInfo.ConnectionState`, the base port,
+the peer's real remote address. It is not a special case reserved for control
+traffic; it carries its share of data flows like any other lane.
+
+## Socket layout
+
+`routines` is **per port**. Each of `multiport.ports` consecutive ports gets its
+own full group of `routines` sockets sharing it through `SO_REUSEPORT`, so total
+sockets = total routines = total tun queues = `routines * multiport.ports`.
+
+```
+routines: 2, multiport.ports: 3, listen.port: 4242
+
+              port 4242         port 4243         port 4244
+             (lane 0/base)       (lane 1)          (lane 2)
+            +-------------+   +-------------+   +-------------+
+ writers[]  |  0  |  1    |   |  2  |  3    |   |  4  |  5    |
+            +-------------+   +-------------+   +-------------+
+ routine        0     1           0     1           0     1
+```
+
+Sockets are laid out **port-major**: `writers[s*routinesPerPort + r]` is the
+r'th socket on port `listen.port+s`. So:
+
+```go
+laneSock(q, s) = s*routinesPerPort + q%routinesPerPort   // inside.go
+egressSock(q)  = laneSock(q, 0)                          // base traffic
+```
+
+Two properties fall out of this, and the rest of the design depends on both:
+
+1. **Every routine owns exactly one socket.** `listenIn` blocks in `recvmmsg`
+   and everything downstream of it -- the batcher, the conntrack cache, the
+   `txQueue` -- is single-owner and lock-free. More sockets than routines would
+   need epoll or locks.
+2. **Every routine has a sibling socket at the same group position on every
+   port.** So socket selection is a pure function of `(queue, lane)` with no
+   borrowing and no shared state, and each port's traffic spreads across its
+   whole group rather than funnelling into one socket.
+
+The second property is why `routines` is per port rather than a total to divide
+up. With one socket per port, each port would be served by a single core -- worst
+of all the base port, which carries every handshake, every lighthouse and punch
+packet, every peer without multiport, and every tunnel whose lanes are down.
+
+## Negotiation
+
+Multiport capability rides the existing handshake payload as two new protobuf
+fields (`handshake/payload.go`): `InitiatorLanes` field 9 and `ResponderLanes`
+field 10, each a `LaneDetails{PortCount, BasePort, TxLanes}`.
+
+- `PortCount` / `BasePort` -- the contiguous port range the sender bound, so the
+  peer knows where to aim its lanes.
+- `TxLanes` -- how many lanes the sender may send on, so the peer knows how many
+  lane sessions it must be prepared to receive on.
+
+Both are `nil` when multiport is off, which keeps the encoded payload
+**byte-identical** to a vanilla one. A peer that has never heard of lanes skips
+unknown fields as protobuf requires, and gets a plain tunnel.
+
+From the result, `newLaneSet` computes:
+
+```go
+sessions  = min(max(myLanes, peerTxLanes), 256)  // we must be able to RECEIVE all of theirs
+txLanes   = min(myLanes, peerPortCount, sessions) // we may only SEND on ports they bound
+```
+
+Sizing RX by the peer's count and TX by our own is what lets asymmetric hosts
+work: a 4-port laptop talking to a 32-port server sends on 4 lanes and receives
+on 32.
+
+### Port pairing
+
+Lane `s` targets `peerBasePort + ((s + portOffset) % peerPortCount)`.
+
+`portOffset` is a per-pair FNV hash of the sorted vpn-address pair. Without it,
+every small peer would aim its few lanes at a big peer's first few ports and
+concentrate that peer's receive work on a couple of sockets.
+
+The rotation has to cancel, though, or the two directions of one flow would take
+unrelated 4-tuples and neither side's traffic would arrive through the conntrack
+or NAT entry the other's probe opened. So both sides hash the *same* sorted pair
+and the higher-addressed side **negates** the result. When the port counts match,
+the two rotations cancel exactly: our lane `s`'s 4-tuple is the reverse of the
+peer's lane `s`. `laneBias` does the matching rotation on the flow hash for the
+same reason.
+
+That pairing only exists when our lane indices map one-to-one onto the peer's
+ports, which is exactly the `txLanes == peerPortCount` test `newLaneSet` applies
+before setting `laneBias`. If we send on 4 lanes and the peer bound 8 ports, four
+of its ports have no lane of ours pointing at them, and no choice of rotation can
+make our lane `s` and its lane `s` be each other's reverse. So in that case
+`laneBias` stays 0 and each side hashes the flow to a lane on its own. The flow
+still works and is still spread; the two directions simply take two unrelated
+4-tuples instead of one 4-tuple and its exact reverse, and each direction depends
+on its own lane's probe having opened its own conntrack or NAT entry.
+
+## Bringing a lane up
+
+Receiving on a lane needs no permission: the keys are derivable the moment the
+base handshake completes. **Sending** on one needs proof the new 4-tuple actually
+works, because nothing else would notice a middlebox quietly dropping it. So:
+
+```
+lane down  --probe (Test/LaneProbe on lane s, from port base+s to peer's lane port)-->
+           <--ack (Test/LaneProbeAck, on the BASE tunnel)--
+lane up
+```
+
+- The probe is encrypted with **the lane's own session**, so an ack proves the
+  whole lane end to end: our source port reached the peer, its reply reached us,
+  and the keys we derived match the ones it derived.
+- The ack rides the **base tunnel** on purpose. A probe proves the peer's lane
+  works in *its* send direction; answering on our own lane `s` would make the
+  result depend on a second path that can be broken independently.
+- The ack echoes the header's lane, not the payload's, so a peer cannot get us to
+  vouch for a lane it did not probe.
+- A generation byte in the probe is echoed in the ack, so a late ack cannot
+  promote a lane on the strength of a superseded probe.
+
+`txAddr[s]` is a single `atomic.Pointer[netip.AddrPort]` that is *both* the TX
+gate and the destination, so a data-plane routine that loads non-nil has
+everything it needs in one atomic read and there is no window where one is set
+and the other is not.
+
+Probing is driven by the connection manager's per-tunnel traffic tick
+(`maintainLanes` -> `probeLanes`), which only fires for a tunnel with traffic --
+the same condition that makes a lane worth having. Timers:
+
+| timer | value |
+|---|---|
+| probe timeout | 2s (shorter than the 5s tick on purpose) |
+| keepalive | 30s |
+| retry backoff | 5s, doubling to 60s |
+| max failure count | 8 |
+
+Traffic on a lane is not evidence the lane works -- that is the whole reason
+lanes need probing -- so a lane that silently breaks is only caught by the
+keepalive.
+
+Every lane starts out **demanded**, so the first traffic tick probes all of them
+at once. This matters more than it looks: see "flow pinning" below. A lane that
+is down also raises demand from the TX path each time a flow wants it, so a
+lane that keeps failing is retried only while something still wants it, and an
+idle tunnel costs nothing.
+
+A lane aims **only** at its own port. There is no fallback to the peer's base
+port when the lane port doesn't answer: a lane sharing the base port's
+destination would gain only a source port of its own while costing the peer the
+receive spread that is the entire point. A lane that can't reach its port stays
+down and its flows ride the base tunnel.
+
+## Flow -> lane -> routine: keeping a flow consistent
+
+This is the part that took the most iterations to get right, so it's worth
+spelling out why it is shaped the way it is.
+
+### The kernel's tun queue feedback loop
+
+On Linux, a multiqueue tun device does not simply hash a flow to a queue. It
+also *learns*: `tun_flow_update` records "this flow was last seen on queue *q*"
+from the packets **we write in**, and `tun_automq_select_queue` prefers what it
+learned over the hash for as long as the flow stays busy.
+
+We write an inbound packet to the tun queue with the same index as the UDP
+routine that received it (`batchers[rxc.q]`). So the queue a flow's *outbound*
+packets arrive on is decided by the socket its *inbound* packets landed on, at
+the far end, one RTT ago.
+
+### Why the lane comes from the flow, not the routine
+
+The obvious design -- routine `q` sends on lane `q` -- deadlocks against that
+feedback loop:
+
+1. A tunnel comes up. All lanes are down, so all traffic goes out lane 0.
+2. The peer receives it all on socket 0 and writes it all to tun queue 0.
+3. Both kernels now believe every flow belongs on queue 0.
+4. Every flow is read by routine 0, so every flow picks lane 0.
+5. Go to 2. The tunnel is pinned to lane 0 for as long as its flows stay busy.
+
+So the lane comes from **the flow's own 5-tuple**, not from the routine index:
+
+```go
+s = (laneFlowHash(fwPacket) + laneBias) % txLanes    // lanes.go:txLaneForFlow
+```
+
+This makes lane spread completely independent of how the kernel steers tun
+queues. It also gives the properties you actually want from a flow's point of
+view:
+
+- **A flow stays on one lane for its life.** The hash is a pure function of the
+  5-tuple, so there is no per-packet lane hopping and therefore no reordering
+  introduced by multiport.
+- **One lane's replay window sees one stable set of flows.**
+- **Both directions of a flow pick partner lanes.** `laneFlowHash` orders the two
+  endpoints before hashing, so it returns the same value from either end, and
+  `laneBias` lines the two sides' choices up. The two directions are exact
+  reverse 4-tuples, which is what NAT and stateful firewalls need.
+
+`newLaneSet` demanding every lane up front is the other half of this. Lanes have
+to be up *before* the flows are: a flow that starts while the lanes are still
+down gets its queue pinned by step 2 above and can stay there for its whole
+life. Eager demand costs one probe per lane on any tunnel that has traffic, and
+nothing at all on one that doesn't.
+
+### The full path
+
+```
+  outbound                                     inbound (at the peer)
+  --------                                     ---------------------
+  inside flow
+     |  kernel tun hash, or the queue it
+     |  learned from our last write
+     v
+  tun queue q  ->  routine q
+     |
+     |  s = laneFlowHash(flow) % txLanes      lane s arrives on port base+s
+     v                                           |
+  lane s session                                 |  SO_REUSEPORT hash of the
+     |                                           |  4-tuple picks one socket
+     |  writers[laneSock(q,s)]                   v
+     v                                       routine q' (owner of that socket)
+  port base+s  ------------------------->        |
+                                                 v
+                                             tun queue q'  (teaches the kernel
+                                                            flow -> q')
+```
+
+Note that RX is entirely socket-agnostic: the lane comes from the header byte,
+not from the port the packet arrived on, and roaming is skipped for `lane != 0`
+(a lane's source address is a per-lane 4-tuple, not the tunnel's remote -- letting
+it roam the hostinfo would point every non-lane packet at a lane port). So a
+lane packet may legitimately arrive on any socket, which is what makes the
+reuseport spread within a port safe.
+
+### Ordering and locking
+
+Several routines can write to one socket, since the routines whose lane
+arithmetic lands on the same index share it. Linux's `batchWriter` serializes
+`sendmmsg` with a mutex. Per-flow wire order still holds regardless: a flow is
+hashed onto one lane and read by one routine, so nothing else is writing that
+flow.
+
+Each routine holds one `txQueue` with one shared arena (~1.16 MB) and builds a
+`SendBatch` per lane lazily, on the first packet that picks it, so a routine that
+never sends on a lane never pays for one.
+
+### The FIPS 140 encrypt lock
+
+In FIPS 140 mode -- a `boringcrypto` build, or `GODEBUG=fips140=on` -- nebula
+uses `noiseutil.CipherAESGCMFIPS140` instead of the plain AES-GCM cipher. That
+cipher is the TLS 1.3 GCM (`GCMWithXORCounterNonce`), which **panics** if it is
+asked to seal with a counter that is not strictly greater than the last one. That
+check is the point: it is the nonce-reuse protection FIPS 140 requires, and
+`noiseutil`'s startup self-test refuses to run if the check has gone missing.
+
+The check means encrypts on one session cannot overlap, so
+`noiseutil.EncryptLockNeeded` is true and every send path takes that session's
+`ConnectionState.writeLock`:
+
+```go
+if noiseutil.EncryptLockNeeded {
+        ci.writeLock.Lock()
+}
+c := ci.messageCounter.Add(1)
+out = header.EncodeLane(scratch, ..., c, lane)
+out, encErr := ci.eKey.EncryptDanger(out, out, seg, c, nb)
+if noiseutil.EncryptLockNeeded {
+        ci.writeLock.Unlock()
+}
+```
+
+The lock has to cover the seal and not just the counter increment. Reserving
+counters atomically is easy; the requirement is that the seals *arrive at the
+AEAD in counter order*, and only holding the lock across both gives that.
+
+So under FIPS 140 the encrypt cost of a tunnel is pinned to one core. `routines:
+N` gives N readers, but every one of them that has a packet for the same peer
+queues on the same mutex, and with TSO/USO the lock is taken and released once
+per segment -- up to ~45 times for a single superpacket
+(`sendInsideEncrypt`). Receive is not affected: `extractFIPSAEAD` deliberately
+pulls the inner FIPS AEAD out of the `crypto/tls` wrapper because that inner
+implementation is safe to `Open` concurrently, and `decryptLock` is only ever
+held around the replay-window check and update.
+
+Lanes split the lock because a lane is a separate `ConnectionState`: its own
+`writeLock`, its own message counter, its own nonce sequence. A peer we send to
+on `txLanes` lanes has `txLanes` independent encrypt locks, so encrypt for that
+one tunnel can run on that many cores at once.
+
+The flow hash is what makes this work rather than merely legal. A flow maps to
+one lane, so all of a flow's packets take one lock in counter order -- exactly
+what the FIPS AEAD demands -- while different flows to the same peer land on
+different locks. Contention is divided, not eliminated: any routine may send on
+any lane, so two routines whose flows hash to the same lane still serialize
+against each other.
+
+Two caveats. This is only a FIPS 140 benefit -- in a normal build
+`EncryptLockNeeded` is false, encrypt is lock-free, and lanes buy path and queue
+spread only. And it is not unilateral: `txLanes` is bounded by the peer's port
+count, so a peer that binds one port leaves us back on one encrypt lock however
+many ports we bound ourselves.
+
+## Falling back to the old behavior
+
+Multiport degrades rather than failing, at every level. This is deliberate:
+managed deployments can't be hard-errored on config they don't control.
+
+### Whole-node: back to one port
+
+Any of these turns multiport off, logs why, and leaves a node that binds one
+port with `routines` `SO_REUSEPORT` sockets -- bit-for-bit the pre-multiport
+configuration:
+
+| condition | log |
+|---|---|
+| `multiport.enabled: false` | - |
+| `multiport.ports` unset, 0, or 1 | `multiport disabled: set multiport.ports > 1 ...` |
+| `listen.port + ports - 1 > 65535` | `multiport disabled: would bind ports beyond 65535` |
+| platform can't run multiple UDP readers | `multiport disabled: this platform does not support multiple udp readers` |
+| that capability couldn't be probed | `multiport disabled: could not probe udp reader support` |
+
+`multiport.ports` is also clamped to 256 (the lane header limit) and to
+`maxRoutines / routines`, with a warning, rather than being rejected.
+
+With a dynamic `listen.port: 0`, the first socket binds dynamically and the
+range is claimed above it; a partially-occupied range re-rolls with a fresh
+dynamic port up to 6 times.
+
+`laneSock` collapses to the identity when multiport is off, so the send path is
+unchanged: a routine writes to its own socket and no lane batches are built at
+all.
+
+### Per-tunnel: back to a single session
+
+`newLaneSet` returns `nil`, and the tunnel is an ordinary one, when:
+
+- the peer advertised no port count (vanilla peer, or multiport off there), or
+- `sessions < 2`, i.e. neither side offers a lane.
+
+`txLanes` can also land at 1 -- we bound ports but the peer bound only one -- in
+which case the set exists for RX but we never send on a lane.
+
+### Per-packet: back to the base tunnel
+
+`txLaneForFlow` returns a nil session and the packet rides the base tunnel,
+decided per packet with no state to unwind:
+
+- the flow hashed onto lane 0 (its fair share of flows);
+- the lane it hashed onto has never come up;
+- the lane was **demoted** -- a probe or keepalive went unanswered. Fallback is
+  immediate, on the very next packet, and the miss re-raises demand so the lane
+  is re-probed;
+- the tunnel is **relayed** -- lanes are direct-only, so `probeLanes` drops them
+  all when there is no direct path and rebuilds when one returns;
+- the peer **roamed** -- a new NAT mapping has no derivable relationship to the
+  old lane ports, so every lane is torn down and re-probed from a clean backoff.
+  Standing demand is deliberately kept across a reset, so the lanes that were
+  actually carrying data come back first.
+
+### Always on the base tunnel
+
+Handshakes, lighthouse traffic, punching, relay carriers, close packets, rejects,
+and lane probe *acks* all use the base session and a socket on the base port
+(`egressSock`). Base traffic must keep the base source port or a vanilla peer
+would see the tunnel's address move and roam-thrash.
+
+`recv_error` is the one deliberate exception: it replies from the socket the
+offending packet arrived on, because a lane peer's spoof guard compares our
+source address against that lane's remote and would discard a reply from the
+base port.
+
+### Wire compatibility
+
+- A vanilla sender emits lane 0 in a field it thinks is reserved, and lane 0 is
+  the base tunnel, so it reads correctly with no version check.
+- We always send the upper 8 reserved bits as zero.
+- A lane index above what this tunnel has (a stale lane from a rolled tunnel, or
+  a peer sending above what it advertised) is dropped **silently** -- a
+  `recv_error` would tear down a perfectly good base tunnel on the strength of
+  one odd packet.
+- Lane ciphertext wrapped in a relay carrier is refused before the session
+  lookup, so a junk relay packet can't make us derive a session.
+
+## Security notes
+
+- The lane index is in the AEAD's associated data, so it is authenticated, not
+  just carried.
+- On RX, a lane session derived for an unrecognized lane is **not installed**
+  until the packet actually decrypts. Anyone who can spoof this tunnel's local
+  index can name any lane; installing on sight would let them make us hold a
+  replay window and two cipher states per lane, per tunnel, for lanes they never
+  send on.
+- Two routines racing on a lane's first packet each derive a session. The loser's
+  is dropped, and its replay-window entry for the packet it just accepted is
+  handed to the winner (`installSession`) -- the keys are identical, so it is the
+  same window in every respect that matters.
+
+## Configuration
+
+```yaml
+routines: 8          # PER PORT under multiport; total workers = routines * ports
+multiport:
+  enabled: true      # default true, but inert without ports
+  ports: 4           # consecutive ports from listen.port; must be > 1, no default
+  lanes: 0           # 0 = one per bound port; lower to send on a subset
+```
+
+`multiport.ports` has no default on purpose: under these semantics a default
+would silently multiply the worker count. Nothing here is reloadable.
+
+Both sides need a port range, and the range
+`[listen.port, listen.port+ports-1]` must be open in both directions. Opening
+only the base port is the common failure and gives you exactly one working lane
+-- the one whose rotation happens to land on the base port.
+
+## Observability
+
+```
+nebula-ssh> print-tunnel -vpn-addr <peer>
+```
+
+`lanes[]` gives per-lane `up`, `remote` and `messageCounter`, which is the fastest
+way to tell "no lanes negotiated" (key absent) from "lanes up but traffic on one"
+(counters).
+
+Metrics, registered only when multiport is running so they don't sit at zero on
+nodes without it:
+
+- `multiport.lanes.up` -- lanes currently carrying traffic
+- `multiport.lanes.tunnels` -- tunnels with any lanes
+
+Both are counted by walking the hostmap rather than kept at promotion/demotion,
+because a counter would drift upward forever: a tunnel torn down with its lanes
+up never demotes them.
+
+Logs worth grepping: `multiport enabled` and `multiport routines` at startup, the
+`lanes` attr on handshake completion (`tx`, `sessions`, `peerBasePort`,
+`peerPorts`, `portOffset`), and `Multiport lane up` / `Multiport lane demoted`,
+both of which name the `udpAddr` involved.
+
+## Known gaps
+
+- No `readOutsidePackets`-level test for the RX lane drop paths.
+- No multiport coverage in the e2e suite.
+- `routines * ports > 256` fails at startup from the kernel's tun queue limit
+  rather than being clamped with a warning.

dns_server.go

@@ -97,8 +97,7 @@ func (d *dnsServer) reload(c *config.C, initial bool) error {
 	newAddr := getDnsServerAddr(c)
 
 	d.serverMu.Lock()
-	running := d.server
-	runningStarted := d.started
+	running := d.server != nil
 	sameAddr := d.addr == newAddr
 	d.addr = newAddr
 	d.enabled.Store(enabled)
@@ -112,7 +111,7 @@ func (d *dnsServer) reload(c *config.C, initial bool) error {
 	}
 
 	if !enabled {
-		if running != nil {
+		if running {
 			d.Stop()
 		}
 		// Drop any records that accumulated while enabled; a later re-enable
@@ -121,12 +120,12 @@ func (d *dnsServer) reload(c *config.C, initial bool) error {
 		return nil
 	}
 
-	if running == nil {
+	if !running {
 		// Was disabled (or never started); bring it up now.
 		go d.Start()
 	} else if !sameAddr {
-		d.shutdownServer(running, runningStarted, "reload")
-		// Old Start goroutine has now exited; bring up a fresh listener on the new address.
+		// Stop clears the slot before shutting down, otherwise the Start below can find the dying server and refuse
+		d.Stop()
 		go d.Start()
 	}
 
@@ -162,7 +161,9 @@ func (d *dnsServer) Start() {
 
 	started := make(chan struct{})
 	d.serverMu.Lock()
-	if d.ctx.Err() != nil {
+	// Re-check enabled under the lock, a disable that raced our check above snapshots the slot under it too.
+	// Two reloads in quick succession can both spawn a Start, the loser would orphan the live listener past Stop
+	if d.ctx.Err() != nil || d.server != nil || !d.enabled.Load() {
 		d.serverMu.Unlock()
 		return
 	}
@@ -200,6 +201,14 @@ func (d *dnsServer) Start() {
 		close(started)
 	}
 
+	// Release our slot, unless a reload already replaced us, so a dead listener can't block a future Start
+	d.serverMu.Lock()
+	if d.server == server {
+		d.server = nil
+		d.started = nil
+	}
+	d.serverMu.Unlock()
+
 	if err != nil {
 		d.l.Warn("Failed to run the DNS responder", "error", err)
 	}

dns_server_test.go

@@ -194,14 +194,51 @@ func TestDnsServer_reload_initial_serveDnsWithoutLighthouse(t *testing.T) {
 }
 
 func TestDnsServer_reload_sameAddr_noOp(t *testing.T) {
+	port := freeUDPPort(t)
 	ds, c := newTestDnsServer(t)
-	setDnsConfig(c, "127.0.0.1", "0", true, true)
-
+	setDnsConfig(c, "127.0.0.1", port, true, true)
 	require.NoError(t, ds.reload(c, true))
-	// No server running yet, no addr change. Reload should not spawn anything.
+
+	go ds.Start()
+	waitForBind(t, ds)
+
+	ds.serverMu.Lock()
+	before := ds.server
+	ds.serverMu.Unlock()
+	require.NotNil(t, before)
+
+	// Same address, so the running listener must be left alone rather than rebuilt under live queries
 	require.NoError(t, ds.reload(c, false))
 	assert.True(t, ds.enabled.Load())
-	assert.Nil(t, ds.server)
+
+	ds.serverMu.Lock()
+	after := ds.server
+	ds.serverMu.Unlock()
+	assert.Same(t, before, after, "a same-address reload must not restart the listener")
+
+	ds.Stop()
+}
+
+// The branch the old sameAddr test was accidentally hitting: enabled with nothing running means reload starts it.
+func TestDnsServer_reload_whenNotRunning_starts(t *testing.T) {
+	port := freeUDPPort(t)
+	ds, c := newTestDnsServer(t)
+	setDnsConfig(c, "127.0.0.1", port, true, true)
+
+	// initial only records config, it never starts anything
+	require.NoError(t, ds.reload(c, true))
+	ds.serverMu.Lock()
+	assert.Nil(t, ds.server, "the initial reload must not start a listener")
+	ds.serverMu.Unlock()
+
+	require.NoError(t, ds.reload(c, false))
+	waitForBind(t, ds)
+
+	ds.serverMu.Lock()
+	assert.NotNil(t, ds.server, "a reload with nothing running should bring DNS up")
+	ds.serverMu.Unlock()
+
+	ds.Stop()
 }
 
 func TestDnsServer_StartStop_lifecycle(t *testing.T) {
@@ -427,3 +464,168 @@ func waitFor(t *testing.T, cond func() bool) {
 	}
 	t.Fatal("timed out waiting for condition")
 }
+
+// Two reloads in quick succession, or a HUP before Control.Start, can race two Starts at the same listener.
+func TestDnsServer_Start_isIdempotent(t *testing.T) {
+	port := freeUDPPort(t)
+	ds, c := newTestDnsServer(t)
+	setDnsConfig(c, "127.0.0.1", port, true, true)
+	require.NoError(t, ds.reload(c, true))
+
+	go ds.Start()
+	waitForBind(t, ds)
+
+	ds.serverMu.Lock()
+	first := ds.server
+	ds.serverMu.Unlock()
+	require.NotNil(t, first)
+
+	// If the second Start replaces the tracked server, Stop kills the wrong one and the port leaks
+	done := make(chan struct{})
+	go func() {
+		ds.Start()
+		close(done)
+	}()
+	select {
+	case <-done:
+	case <-time.After(time.Second * 5):
+		t.Fatal("second Start never returned")
+	}
+
+	ds.serverMu.Lock()
+	second := ds.server
+	ds.serverMu.Unlock()
+	assert.Same(t, first, second, "a second Start must not replace the running server")
+
+	// The real proof, after Stop the port must actually be free
+	ds.Stop()
+	waitFor(t, func() bool {
+		pc, err := net.ListenPacket("udp", "127.0.0.1:"+port)
+		if err != nil {
+			return false
+		}
+		_ = pc.Close()
+		return true
+	})
+}
+
+// An address change must actually end up listening on the new port. Start's guard refuses when a server is already
+// installed, so reload has to clear the slot before shutting the old one down.
+func TestDnsServer_reload_addrChange_restarts(t *testing.T) {
+	first := freeUDPPort(t)
+	second := freeUDPPort(t)
+
+	ds, c := newTestDnsServer(t)
+	setDnsConfig(c, "127.0.0.1", first, true, true)
+	require.NoError(t, ds.reload(c, true))
+
+	go ds.Start()
+	waitForBind(t, ds)
+
+	// Cycle a few times, the failure this guards against depends on which goroutine wins serverMu
+	for i := range 8 {
+		want := second
+		if i%2 == 1 {
+			want = first
+		}
+		setDnsConfig(c, "127.0.0.1", want, true, true)
+		require.NoError(t, ds.reload(c, false))
+		waitForBind(t, ds)
+
+		ds.serverMu.Lock()
+		srv := ds.server
+		ds.serverMu.Unlock()
+		require.NotNil(t, srv, "reload left DNS down instead of restarting it")
+		require.Equal(t, "127.0.0.1:"+want, srv.Addr, "reload should be serving the new address")
+	}
+
+	// Land back on second so the port assertions below are meaningful
+	setDnsConfig(c, "127.0.0.1", second, true, true)
+	require.NoError(t, ds.reload(c, false))
+	waitForBind(t, ds)
+
+	// The old port must be released and the new one actually held
+	waitFor(t, func() bool {
+		pc, err := net.ListenPacket("udp", "127.0.0.1:"+first)
+		if err != nil {
+			return false
+		}
+		_ = pc.Close()
+		return true
+	})
+	_, err := net.ListenPacket("udp", "127.0.0.1:"+second)
+	require.Error(t, err, "the new address should be bound by the DNS responder")
+
+	ds.Stop()
+}
+
+// A listener that dies on its own must release the slot, or a later same-addr reload sees it as running and no-ops.
+func TestDnsServer_Start_bindFailure_releasesSlot(t *testing.T) {
+	port := freeUDPPort(t)
+	blocker, err := net.ListenPacket("udp", "127.0.0.1:"+port)
+	require.NoError(t, err)
+
+	ds, c := newTestDnsServer(t)
+	setDnsConfig(c, "127.0.0.1", port, true, true)
+	require.NoError(t, ds.reload(c, true))
+
+	ds.Start() // returns once the bind fails
+
+	ds.serverMu.Lock()
+	assert.Nil(t, ds.server, "a listener that failed to bind must not stay parked in the slot")
+	ds.serverMu.Unlock()
+
+	// With the slot released, a reload can retry once the port frees up
+	require.NoError(t, blocker.Close())
+	require.NoError(t, ds.reload(c, false))
+	waitForBind(t, ds)
+
+	ds.serverMu.Lock()
+	assert.NotNil(t, ds.server, "a same-addr reload should retry after a failed bind")
+	ds.serverMu.Unlock()
+
+	ds.Stop()
+}
+
+// A disable that lands while Start is between its unlocked check and the guard must not leave a listener behind.
+func TestDnsServer_Start_refusesWhenDisabledUnderLock(t *testing.T) {
+	port := freeUDPPort(t)
+	ds, c := newTestDnsServer(t)
+	setDnsConfig(c, "127.0.0.1", port, true, true)
+	require.NoError(t, ds.reload(c, true))
+	require.True(t, ds.enabled.Load())
+
+	// Holding serverMu parks Start on the lock, the only way to land the disable in that window on purpose
+	ds.serverMu.Lock()
+
+	done := make(chan struct{})
+	go func() {
+		ds.Start()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+		ds.serverMu.Unlock()
+		t.Fatal("Start returned early, the test never exercised the window")
+	case <-time.After(time.Millisecond * 100):
+	}
+
+	// The disable reload's critical section. It sees nothing running, so it never calls Stop.
+	ds.enabled.Store(false)
+	ds.serverMu.Unlock()
+
+	select {
+	case <-done:
+	case <-time.After(time.Second * 5):
+		t.Fatal("Start never returned")
+	}
+
+	ds.serverMu.Lock()
+	assert.Nil(t, ds.server, "Start must not install a listener a disable already cancelled")
+	ds.serverMu.Unlock()
+
+	pc, err := net.ListenPacket("udp", "127.0.0.1:"+port)
+	require.NoError(t, err, "an orphaned listener is still holding the port")
+	_ = pc.Close()
+}

e2e/handshakes_test.go

@@ -405,7 +405,7 @@ func TestStage1Race(t *testing.T) {
 
 	r.Log("Spin until connection manager tears down a tunnel")
 
-	for len(myControl.GetHostmap().Indexes)+len(theirControl.GetHostmap().Indexes) > 2 {
+	for myControl.GetHostmapIndexCount()+theirControl.GetHostmapIndexCount() > 2 {
 		assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
 		t.Log("Connection manager hasn't ticked yet")
 		time.Sleep(time.Second)
@@ -453,9 +453,11 @@ func TestUncleanShutdownRaceLoser(t *testing.T) {
 
 	r.Log("Nuke my hostmap")
 	myHostmap := myControl.GetHostmap()
+	myHostmap.Lock()
 	myHostmap.Hosts = map[netip.Addr]*nebula.HostInfo{}
 	myHostmap.Indexes = map[uint32]*nebula.HostInfo{}
 	myHostmap.RemoteIndexes = map[uint32]*nebula.HostInfo{}
+	myHostmap.Unlock()
 
 	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("Hi from me again")))
 	p = r.RouteForAllUntilTxTun(theirControl)
@@ -465,10 +467,10 @@ func TestUncleanShutdownRaceLoser(t *testing.T) {
 	assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
 
 	r.Log("Wait for the dead index to go away")
-	start := len(theirControl.GetHostmap().Indexes)
+	start := theirControl.GetHostmapIndexCount()
 	for {
 		assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
-		if len(theirControl.GetHostmap().Indexes) < start {
+		if theirControl.GetHostmapIndexCount() < start {
 			break
 		}
 		time.Sleep(time.Second)
@@ -504,9 +506,11 @@ func TestUncleanShutdownRaceWinner(t *testing.T) {
 
 	r.Log("Nuke my hostmap")
 	theirHostmap := theirControl.GetHostmap()
+	theirHostmap.Lock()
 	theirHostmap.Hosts = map[netip.Addr]*nebula.HostInfo{}
 	theirHostmap.Indexes = map[uint32]*nebula.HostInfo{}
 	theirHostmap.RemoteIndexes = map[uint32]*nebula.HostInfo{}
+	theirHostmap.Unlock()
 
 	theirControl.InjectTunPacket(BuildTunUDPPacket(myVpnIpNet[0].Addr(), 80, theirVpnIpNet[0].Addr(), 80, []byte("Hi from them again")))
 	p = r.RouteForAllUntilTxTun(myControl)
@@ -517,10 +521,10 @@ func TestUncleanShutdownRaceWinner(t *testing.T) {
 	assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
 
 	r.Log("Wait for the dead index to go away")
-	start := len(myControl.GetHostmap().Indexes)
+	start := myControl.GetHostmapIndexCount()
 	for {
 		assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
-		if len(myControl.GetHostmap().Indexes) < start {
+		if myControl.GetHostmapIndexCount() < start {
 			break
 		}
 		time.Sleep(time.Second)
@@ -628,10 +632,10 @@ func TestReestablishRelays(t *testing.T) {
 	r.Log("Close the tunnel")
 	relayControl.CloseTunnel(theirVpnIpNet[0].Addr(), true)
 
-	start := len(myControl.GetHostmap().Indexes)
-	curIndexes := len(myControl.GetHostmap().Indexes)
+	start := myControl.GetHostmapIndexCount()
+	curIndexes := myControl.GetHostmapIndexCount()
 	for curIndexes >= start {
-		curIndexes = len(myControl.GetHostmap().Indexes)
+		curIndexes = myControl.GetHostmapIndexCount()
 		r.Logf("Wait for the dead index to go away:start=%v indexes, current=%v indexes", start, curIndexes)
 		myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("Hi from me should fail")))
 
@@ -721,6 +725,70 @@ func TestReestablishRelays(t *testing.T) {
 
 }
 
+func TestRelayHandshakeOverDisestablishedEntry(t *testing.T) {
+	t.Parallel()
+	// If them tears down the tunnel while me keeps Established relay state, me's next
+	// handshake flows through the relay with no fresh CreateRelayRequest and lands on
+	// them's Disestablished terminal relay entry. them must re-establish that entry, or
+	// its first transmit deletes its only relay and the tunnel is born transmit-dead:
+	// them can receive but every send is silently dropped.
+	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version1, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})
+	myControl, myVpnIpNet, _, _ := newSimpleServer(cert.Version1, ca, caKey, "me     ", "10.128.0.1/24", m{"relay": m{"use_relays": true}})
+	relayControl, relayVpnIpNet, relayUdpAddr, _ := newSimpleServer(cert.Version1, ca, caKey, "relay  ", "10.128.0.128/24", m{"relay": m{"am_relay": true}})
+	theirControl, theirVpnIpNet, theirUdpAddr, _ := newSimpleServer(cert.Version1, ca, caKey, "them   ", "10.128.0.2/24", m{"relay": m{"use_relays": true}})
+
+	// Teach my how to get to the relay and that their can be reached via the relay
+	myControl.InjectLightHouseAddr(relayVpnIpNet[0].Addr(), relayUdpAddr)
+	myControl.InjectRelays(theirVpnIpNet[0].Addr(), []netip.Addr{relayVpnIpNet[0].Addr()})
+	relayControl.InjectLightHouseAddr(theirVpnIpNet[0].Addr(), theirUdpAddr)
+
+	// Build a router so we don't have to reason who gets which packet
+	r := router.NewR(t, myControl, relayControl, theirControl)
+	defer r.RenderFlow()
+
+	// Start the servers
+	myControl.Start()
+	relayControl.Start()
+	theirControl.Start()
+
+	t.Log("Trigger a handshake from me to them via the relay")
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("Hi from me")))
+
+	p := r.RouteForAllUntilTxTun(theirControl)
+	assertUdpPacket(t, []byte("Hi from me"), p, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), 80, 80)
+	oldIdx := myControl.GetHostInfoByVpnAddr(theirVpnIpNet[0].Addr(), false).LocalIndex
+
+	t.Log("Close the tunnel on them only, marking their relay entry Disestablished")
+	theirControl.CloseTunnel(myVpnIpNet[0].Addr(), true)
+
+	t.Log("Re-handshake from me, riding the still-Established relay state")
+	myControl.ReHandshake(theirVpnIpNet[0].Addr())
+	for {
+		h := myControl.GetHostInfoByVpnAddr(theirVpnIpNet[0].Addr(), false)
+		if h != nil && h.LocalIndex != oldIdx && h.RemoteIndex != 0 {
+			break
+		}
+		r.RouteForAllExitFunc(func(*udp.Packet, *nebula.Control) router.ExitType {
+			return router.RouteAndExit
+		})
+	}
+
+	hAtThem := theirControl.GetHostInfoByVpnAddr(myVpnIpNet[0].Addr(), false)
+	require.NotNil(t, hAtThem, "them should have completed the relayed handshake")
+	require.Equal(t, []netip.Addr{relayVpnIpNet[0].Addr()}, hAtThem.CurrentRelaysToMe, "them should know a relay for the new tunnel")
+
+	t.Log("Send from them to me; their only relay entry must survive the transmit")
+	theirControl.InjectTunPacket(BuildTunUDPPacket(myVpnIpNet[0].Addr(), 80, theirVpnIpNet[0].Addr(), 80, []byte("Hi from them")))
+	require.Never(t, func() bool {
+		h := theirControl.GetHostInfoByVpnAddr(myVpnIpNet[0].Addr(), false)
+		return h == nil || len(h.CurrentRelaysToMe) == 0
+	}, time.Second, 10*time.Millisecond, "them deleted its only relay entry; the tunnel is permanently transmit-dead")
+
+	p = r.RouteForAllUntilTxTun(myControl)
+	assertUdpPacket(t, []byte("Hi from them"), p, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), 80, 80)
+	r.RenderHostmaps("Final hostmaps", myControl, relayControl, theirControl)
+}
+
 func TestStage1RaceRelays(t *testing.T) {
 	t.Parallel()
 	//NOTE: this is a race between me and relay resulting in a full tunnel from me to them via relay
@@ -819,18 +887,18 @@ func TestStage1RaceRelays2(t *testing.T) {
 
 	t.Log("Wait until we remove extra tunnels")
 	t.Logf("Waiting for hostinfos to be removed... myControl=%d theirControl=%d relayControl=%d",
-		len(myControl.GetHostmap().Indexes),
-		len(theirControl.GetHostmap().Indexes),
-		len(relayControl.GetHostmap().Indexes),
+		myControl.GetHostmapIndexCount(),
+		theirControl.GetHostmapIndexCount(),
+		relayControl.GetHostmapIndexCount(),
 	)
-	hostInfos := len(myControl.GetHostmap().Indexes) + len(theirControl.GetHostmap().Indexes) + len(relayControl.GetHostmap().Indexes)
+	hostInfos := myControl.GetHostmapIndexCount() + theirControl.GetHostmapIndexCount() + relayControl.GetHostmapIndexCount()
 	retries := 60
 	for hostInfos > 6 && retries > 0 {
-		hostInfos = len(myControl.GetHostmap().Indexes) + len(theirControl.GetHostmap().Indexes) + len(relayControl.GetHostmap().Indexes)
+		hostInfos = myControl.GetHostmapIndexCount() + theirControl.GetHostmapIndexCount() + relayControl.GetHostmapIndexCount()
 		t.Logf("Waiting for hostinfos to be removed... myControl=%d theirControl=%d relayControl=%d",
-			len(myControl.GetHostmap().Indexes),
-			len(theirControl.GetHostmap().Indexes),
-			len(relayControl.GetHostmap().Indexes),
+			myControl.GetHostmapIndexCount(),
+			theirControl.GetHostmapIndexCount(),
+			relayControl.GetHostmapIndexCount(),
 		)
 		assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
 		t.Log("Connection manager hasn't ticked yet")
@@ -924,24 +992,24 @@ func TestRehandshakingRelays(t *testing.T) {
 	assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 	r.RenderHostmaps("working hostmaps", myControl, relayControl, theirControl)
 	// We should have two hostinfos on all sides
-	for len(myControl.GetHostmap().Indexes) != 2 {
-		t.Logf("Waiting for myControl hostinfos (%v != 2) to get cleaned up from lack of use...", len(myControl.GetHostmap().Indexes))
+	for myControl.GetHostmapIndexCount() != 2 {
+		t.Logf("Waiting for myControl hostinfos (%v != 2) to get cleaned up from lack of use...", myControl.GetHostmapIndexCount())
 		r.Log("Assert the relay tunnel still works")
 		assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 		r.Log("yupitdoes")
 		time.Sleep(time.Second)
 	}
 	t.Logf("myControl hostinfos got cleaned up!")
-	for len(theirControl.GetHostmap().Indexes) != 2 {
-		t.Logf("Waiting for theirControl hostinfos (%v != 2) to get cleaned up from lack of use...", len(theirControl.GetHostmap().Indexes))
+	for theirControl.GetHostmapIndexCount() != 2 {
+		t.Logf("Waiting for theirControl hostinfos (%v != 2) to get cleaned up from lack of use...", theirControl.GetHostmapIndexCount())
 		r.Log("Assert the relay tunnel still works")
 		assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 		r.Log("yupitdoes")
 		time.Sleep(time.Second)
 	}
 	t.Logf("theirControl hostinfos got cleaned up!")
-	for len(relayControl.GetHostmap().Indexes) != 2 {
-		t.Logf("Waiting for relayControl hostinfos (%v != 2) to get cleaned up from lack of use...", len(relayControl.GetHostmap().Indexes))
+	for relayControl.GetHostmapIndexCount() != 2 {
+		t.Logf("Waiting for relayControl hostinfos (%v != 2) to get cleaned up from lack of use...", relayControl.GetHostmapIndexCount())
 		r.Log("Assert the relay tunnel still works")
 		assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 		r.Log("yupitdoes")
@@ -1029,24 +1097,24 @@ func TestRehandshakingRelaysPrimary(t *testing.T) {
 	assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 	r.RenderHostmaps("working hostmaps", myControl, relayControl, theirControl)
 	// We should have two hostinfos on all sides
-	for len(myControl.GetHostmap().Indexes) != 2 {
-		t.Logf("Waiting for myControl hostinfos (%v != 2) to get cleaned up from lack of use...", len(myControl.GetHostmap().Indexes))
+	for myControl.GetHostmapIndexCount() != 2 {
+		t.Logf("Waiting for myControl hostinfos (%v != 2) to get cleaned up from lack of use...", myControl.GetHostmapIndexCount())
 		r.Log("Assert the relay tunnel still works")
 		assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 		r.Log("yupitdoes")
 		time.Sleep(time.Second)
 	}
 	t.Logf("myControl hostinfos got cleaned up!")
-	for len(theirControl.GetHostmap().Indexes) != 2 {
-		t.Logf("Waiting for theirControl hostinfos (%v != 2) to get cleaned up from lack of use...", len(theirControl.GetHostmap().Indexes))
+	for theirControl.GetHostmapIndexCount() != 2 {
+		t.Logf("Waiting for theirControl hostinfos (%v != 2) to get cleaned up from lack of use...", theirControl.GetHostmapIndexCount())
 		r.Log("Assert the relay tunnel still works")
 		assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 		r.Log("yupitdoes")
 		time.Sleep(time.Second)
 	}
 	t.Logf("theirControl hostinfos got cleaned up!")
-	for len(relayControl.GetHostmap().Indexes) != 2 {
-		t.Logf("Waiting for relayControl hostinfos (%v != 2) to get cleaned up from lack of use...", len(relayControl.GetHostmap().Indexes))
+	for relayControl.GetHostmapIndexCount() != 2 {
+		t.Logf("Waiting for relayControl hostinfos (%v != 2) to get cleaned up from lack of use...", relayControl.GetHostmapIndexCount())
 		r.Log("Assert the relay tunnel still works")
 		assertTunnel(t, theirVpnIpNet[0].Addr(), myVpnIpNet[0].Addr(), theirControl, myControl, r)
 		r.Log("yupitdoes")
@@ -1123,7 +1191,7 @@ func TestRehandshaking(t *testing.T) {
 	theirConfig.ReloadConfigString(string(rc))
 
 	r.Log("Spin until there is only 1 tunnel")
-	for len(myControl.GetHostmap().Indexes)+len(theirControl.GetHostmap().Indexes) > 2 {
+	for myControl.GetHostmapIndexCount()+theirControl.GetHostmapIndexCount() > 2 {
 		assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
 		t.Log("Connection manager hasn't ticked yet")
 		time.Sleep(time.Second)
@@ -1223,7 +1291,7 @@ func TestRehandshakingLoser(t *testing.T) {
 	myConfig.ReloadConfigString(string(rc))
 
 	r.Log("Spin until there is only 1 tunnel")
-	for len(myControl.GetHostmap().Indexes)+len(theirControl.GetHostmap().Indexes) > 2 {
+	for myControl.GetHostmapIndexCount()+theirControl.GetHostmapIndexCount() > 2 {
 		assertTunnel(t, myVpnIpNet[0].Addr(), theirVpnIpNet[0].Addr(), myControl, theirControl, r)
 		t.Log("Connection manager hasn't ticked yet")
 		time.Sleep(time.Second)

e2e/helpers_test.go

@@ -4,15 +4,13 @@
 package e2e
 
 import (
-	"io"
+	"log/slog"
 	"net/netip"
 	"os"
 	"strings"
 	"testing"
 	"time"
 
-	"log/slog"
-
 	"dario.cat/mergo"
 	"github.com/google/gopacket"
 	"github.com/google/gopacket/layers"
@@ -382,7 +380,7 @@ func getAddrs(ns []netip.Prefix) []netip.Addr {
 func NewTestLogger() *slog.Logger {
 	v := os.Getenv("TEST_LOGS")
 	if v == "" {
-		return slog.New(slog.NewTextHandler(io.Discard, nil))
+		return slog.New(slog.DiscardHandler)
 	}
 
 	level := slog.LevelInfo

e2e/rebind_test.go

@@ -0,0 +1,282 @@
+//go:build e2e_testing
+// +build e2e_testing
+
+package e2e
+
+import (
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/slackhq/nebula"
+	"github.com/slackhq/nebula/cert"
+	"github.com/slackhq/nebula/cert_test"
+	"github.com/slackhq/nebula/e2e/router"
+	"github.com/slackhq/nebula/header"
+	"github.com/slackhq/nebula/udp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// reportedAddrs is what the lighthouse would hand a peer asking where vpnAddr is.
+func reportedAddrs(t *testing.T, lh *nebula.Control, vpnAddr netip.Addr) []netip.AddrPort {
+	t.Helper()
+	cm := lh.QueryLighthouse(vpnAddr)
+	if cm == nil {
+		return nil
+	}
+	var out []netip.AddrPort
+	for _, c := range *cm {
+		out = append(out, c.Reported...)
+		out = append(out, c.Learned...)
+	}
+	return out
+}
+
+// waitForLighthouseMsg routes until a lighthouse message lands on lh, or gives up. Reports whether one arrived.
+func waitForLighthouseMsg(t *testing.T, r *router.R, lh *nebula.Control, wait time.Duration) bool {
+	t.Helper()
+	h := &header.H{}
+	return r.RouteForAllExitFuncOrTimeout(wait, func(p *udp.Packet, c *nebula.Control) router.ExitType {
+		if c != lh {
+			return router.KeepRouting
+		}
+		// Punches are a single byte and never parse, they are just not what we are after
+		if err := h.Parse(p.Data); err != nil {
+			return router.KeepRouting
+		}
+		if h.Type == header.LightHouse {
+			return router.RouteAndExit
+		}
+		return router.KeepRouting
+	})
+}
+
+// A laptop that changes networks has to tell the lighthouse promptly, otherwise the lighthouse keeps handing peers
+// the old address and their punches land nowhere. On a long lighthouse interval the only thing that closes that
+// window is the rebind, which on darwin the network change monitor drives. The e2e build compiles the monitor out,
+// so we call RebindUDPServer directly, which is the same thing the monitor does.
+func TestRebindSendsLighthouseUpdate(t *testing.T) {
+	t.Parallel()
+	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})
+
+	lhControl, lhVpnIpNet, lhUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "lh", "10.128.0.1/24", m{
+		"lighthouse": m{"am_lighthouse": true},
+	})
+
+	// 600s interval, so nothing scheduled can send an update during this test. A rebind is the only thing that can.
+	myControl, _, _, _ := newSimpleServer(cert.Version2, ca, caKey, "me", "10.128.0.2/24", m{
+		"lighthouse": m{
+			"hosts":    []any{lhVpnIpNet[0].Addr().String()},
+			"interval": 600,
+		},
+		"static_host_map": m{
+			lhVpnIpNet[0].Addr().String(): []any{lhUdpAddr.String()},
+		},
+	})
+
+	r := router.NewR(t, lhControl, myControl)
+	defer r.RenderFlow()
+
+	lhControl.Start()
+	myControl.Start()
+
+	// Let the startup registration finish, then clear everything it left behind
+	require.True(t, waitForLighthouseMsg(t, r, lhControl, time.Second*5), "expected an initial registration")
+	r.RouteFor(time.Millisecond * 400)
+
+	// Nothing should be talking to the lighthouse on its own now
+	require.False(t, waitForLighthouseMsg(t, r, lhControl, time.Millisecond*200),
+		"nothing should reach the lighthouse before the rebind")
+
+	myControl.RebindUDPServer()
+
+	assert.True(t, waitForLighthouseMsg(t, r, lhControl, time.Second*5),
+		"a rebind should push an update to the lighthouse rather than waiting out the interval")
+
+	lhControl.Stop()
+	myControl.Stop()
+}
+
+// The other half of a rebind: every live tunnel requeries the lighthouse on its next send. That query is what makes
+// the lighthouse tell the peer to punch toward our new address, which is the part that actually revives a tunnel
+// whose remote NAT state died while we were on a different network.
+func TestRebindRequeriesPeersOnNextSend(t *testing.T) {
+	t.Parallel()
+	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})
+
+	lhControl, lhVpnIpNet, lhUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "lh", "10.128.0.1/24", m{
+		"lighthouse": m{"am_lighthouse": true},
+	})
+
+	lhCfg := m{
+		"lighthouse": m{
+			"hosts":    []any{lhVpnIpNet[0].Addr().String()},
+			"interval": 600,
+			// Without this the peers advertise this machine's real addresses and then try to punch at them,
+			// which the router has no route for.
+			"local_allow_list": m{
+				"10.0.0.0/24": true,
+				"::/0":        false,
+			},
+		},
+		"static_host_map": m{
+			lhVpnIpNet[0].Addr().String(): []any{lhUdpAddr.String()},
+		},
+	}
+
+	myControl, myVpnIpNet, myUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "me", "10.128.0.2/24", lhCfg)
+	theirControl, theirVpnIpNet, theirUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "them", "10.128.0.3/24", lhCfg)
+
+	r := router.NewR(t, lhControl, myControl, theirControl)
+	defer r.RenderFlow()
+
+	lhControl.Start()
+	myControl.Start()
+	theirControl.Start()
+	r.RouteFor(time.Millisecond * 500)
+
+	// Point the peers at each other directly, this test is about the rebind and not about lighthouse discovery
+	myControl.InjectLightHouseAddr(theirVpnIpNet[0].Addr(), theirUdpAddr)
+	theirControl.InjectLightHouseAddr(myVpnIpNet[0].Addr(), myUdpAddr)
+
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("initial")))
+	r.RouteFor(time.Second)
+	require.NotNil(t, myControl.GetHostInfoByVpnAddr(theirVpnIpNet[0].Addr(), false), "expected a tunnel to them")
+	r.RouteFor(time.Millisecond * 300)
+
+	// Assert on what the peer sees rather than on lighthouse traffic. A query for them makes the lighthouse send
+	// them a punch notification, which is the whole point. Our own update to the lighthouse sends them nothing,
+	// so this cannot be satisfied by the update the rebind itself pushes.
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("quiet")))
+	require.False(t, waitForLighthouseMsg(t, r, theirControl, time.Millisecond*300),
+		"an ordinary send should not requery the lighthouse")
+
+	myControl.RebindUDPServer()
+	r.RouteFor(time.Millisecond * 300) // let the update the rebind itself sends pass by
+
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("after rebind")))
+	assert.True(t, waitForLighthouseMsg(t, r, theirControl, time.Second*5),
+		"the first send after a rebind should requery the lighthouse, which then tells the peer to punch at us")
+
+	lhControl.Stop()
+	myControl.Stop()
+	theirControl.Stop()
+}
+
+// The scenario this whole thing exists for: a laptop sleeps at the office and wakes up at home on a new address.
+// Until it tells the lighthouse, the lighthouse keeps handing peers the office address, so their punches land
+// nowhere and the tunnel stays dead. On a long interval the rebind is the only thing that closes that window.
+func TestRebindAdvertisesNewAddressAfterMove(t *testing.T) {
+	t.Parallel()
+	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})
+
+	lhControl, lhVpnIpNet, lhUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "lh", "10.128.0.1/24", m{
+		"lighthouse": m{"am_lighthouse": true},
+	})
+
+	myControl, myVpnIpNet, myUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "me", "10.128.0.2/24", m{
+		"lighthouse": m{
+			"hosts":    []any{lhVpnIpNet[0].Addr().String()},
+			"interval": 600,
+		},
+		"static_host_map": m{
+			lhVpnIpNet[0].Addr().String(): []any{lhUdpAddr.String()},
+		},
+	})
+
+	// Advertise wherever we currently are rather than this machine's real NICs, read fresh each time so a move
+	// is picked up.
+	myControl.SetLocalAddrsFn(func(*nebula.LocalAllowList) []netip.Addr {
+		return []netip.Addr{myControl.GetUDPAddr().Addr()}
+	})
+
+	r := router.NewR(t, lhControl, myControl)
+	defer r.RenderFlow()
+
+	lhControl.Start()
+	myControl.Start()
+
+	require.True(t, waitForLighthouseMsg(t, r, lhControl, time.Second*5), "expected an initial registration")
+	r.RouteFor(time.Millisecond * 400)
+
+	require.Contains(t, reportedAddrs(t, lhControl, myVpnIpNet[0].Addr()), myUdpAddr,
+		"the lighthouse should know the address we started on")
+
+	// Wake up somewhere else
+	newAddr := netip.MustParseAddrPort("10.0.0.99:4242")
+	myControl.SetUDPAddr(newAddr)
+	r.AddRoute(newAddr.Addr(), newAddr.Port(), myControl)
+
+	// Nothing has told the lighthouse, and with interval 600 nothing scheduled will
+	r.RouteFor(time.Millisecond * 400)
+	require.NotContains(t, reportedAddrs(t, lhControl, myVpnIpNet[0].Addr()), newAddr,
+		"the lighthouse should still be handing out the old address before the rebind")
+
+	myControl.RebindUDPServer()
+	require.True(t, waitForLighthouseMsg(t, r, lhControl, time.Second*5), "expected an update after the rebind")
+	r.RouteFor(time.Millisecond * 400)
+
+	assert.Contains(t, reportedAddrs(t, lhControl, myVpnIpNet[0].Addr()), newAddr,
+		"after the rebind the lighthouse should hand peers our new address")
+
+	lhControl.Stop()
+	myControl.Stop()
+}
+
+// A relayed send records traffic but must not consume the rebind epoch. If it does, the next direct send to the
+// relay host sees the epoch already current and never requeries, so the far side is never told to punch at our
+// new address. This pins the SendVia call site, which the unit tests cannot reach.
+func TestRebindRequeriesAfterRelayedSend(t *testing.T) {
+	t.Parallel()
+	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})
+
+	// No lighthouse on purpose: it would hand out a direct address for them and nothing would relay.
+	// Long connection manager timers so it never fires a direct test packet at the relay tunnel and bumps its
+	// epoch mid-test, which is the only other thing that touches that tunnel and would flake the assertion below.
+	myControl, myVpnIpNet, _, _ := newSimpleServer(cert.Version2, ca, caKey, "me", "10.128.0.1/24",
+		m{"relay": m{"use_relays": true}, "timers": m{"connection_alive_interval": 3600, "pending_deletion_interval": 3600}})
+	relayControl, relayVpnIpNet, relayUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "relay", "10.128.0.128/24", m{"relay": m{"am_relay": true}})
+	theirControl, theirVpnIpNet, theirUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "them", "10.128.0.2/24", m{"relay": m{"use_relays": true}})
+
+	myControl.InjectLightHouseAddr(relayVpnIpNet[0].Addr(), relayUdpAddr)
+	myControl.InjectRelays(theirVpnIpNet[0].Addr(), []netip.Addr{relayVpnIpNet[0].Addr()})
+	relayControl.InjectLightHouseAddr(theirVpnIpNet[0].Addr(), theirUdpAddr)
+
+	r := router.NewR(t, myControl, relayControl, theirControl)
+	defer r.RenderFlow()
+
+	myControl.Start()
+	relayControl.Start()
+	theirControl.Start()
+
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("establish")))
+	r.RouteForAllUntilTxTun(theirControl)
+	r.RouteFor(time.Millisecond * 500)
+
+	hi := myControl.GetHostInfoByVpnAddr(theirVpnIpNet[0].Addr(), false)
+	require.NotNil(t, hi, "expected a tunnel to them")
+	require.NotEmpty(t, hi.CurrentRelaysToMe, "them must be reachable only via the relay for this test to mean anything")
+	// sendNoMetrics only reaches SendVia when there is no direct remote, so pin that too. Without this the test
+	// keeps passing while quietly sending direct and never exercising the relay path.
+	require.False(t, hi.CurrentRemote.IsValid(), "them must have no direct remote, otherwise SendVia is never called")
+
+	before, ok := myControl.GetRebindEpochFor(relayVpnIpNet[0].Addr())
+	require.True(t, ok, "expected a tunnel to the relay")
+
+	myControl.RebindUDPServer()
+
+	// Traffic to them goes through SendVia on the relay tunnel. That must record traffic without consuming the
+	// relay tunnel's own epoch edge, which belongs to the direct path.
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("relayed")))
+	r.RouteForAllUntilTxTun(theirControl)
+
+	after, ok := myControl.GetRebindEpochFor(relayVpnIpNet[0].Addr())
+	require.True(t, ok)
+	assert.Equal(t, before, after,
+		"a relayed send consumed the relay tunnel's rebind epoch, so the next direct send will not requery")
+
+	myControl.Stop()
+	relayControl.Stop()
+	theirControl.Stop()
+}

e2e/recovery_timing_test.go

@@ -0,0 +1,136 @@
+//go:build e2e_testing
+// +build e2e_testing
+
+package e2e
+
+import (
+	"testing"
+	"time"
+
+	"github.com/slackhq/nebula"
+	"github.com/slackhq/nebula/cert"
+	"github.com/slackhq/nebula/cert_test"
+	"github.com/slackhq/nebula/e2e/router"
+	"github.com/slackhq/nebula/udp"
+)
+
+// TestRecoveryTiming measures how long a tunnel takes to come back after the peer stops accepting our traffic,
+// which is what a laptop waking on a new network looks like from the peer's side: its NAT has no state for where
+// we are now, so everything we send disappears.
+//
+// It is a measurement, not a pass/fail assertion. Recovery is timed to the moment the peer punches back at us,
+// since that is when its NAT opens and the tunnel is usable again.
+//
+//	go test -tags e2e_testing -v -run TestRecoveryTiming ./e2e/
+func TestRecoveryTiming(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		rebind bool
+	}{
+		{"no trigger", false},
+		{"rebind counter", true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			d, lost := measureRecovery(t, tc.rebind)
+			t.Logf("RESULT %-16s recovered in %-9v (%d packets lost)", tc.name, d.Round(time.Millisecond), lost)
+		})
+	}
+}
+
+// measureRecovery returns how long until the peer punched back, and how many of our packets died meanwhile. When
+// rebind is true we call RebindUDPServer once the tunnel goes dark, which is what the darwin network change
+// monitor does and what iOS has always done. When false, nothing tells nebula anything is wrong.
+func measureRecovery(t *testing.T, rebind bool) (time.Duration, int) {
+	t.Helper()
+	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})
+
+	lhControl, lhVpnIpNet, lhUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "lh", "10.128.0.1/24", m{
+		"lighthouse": m{"am_lighthouse": true},
+	})
+
+	peerCfg := m{
+		"lighthouse": m{
+			"hosts":    []any{lhVpnIpNet[0].Addr().String()},
+			"interval": 600,
+			"local_allow_list": m{
+				"10.0.0.0/24": true,
+				"::/0":        false,
+			},
+		},
+		"static_host_map": m{
+			lhVpnIpNet[0].Addr().String(): []any{lhUdpAddr.String()},
+		},
+	}
+
+	myControl, myVpnIpNet, myUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "me", "10.128.0.2/24", peerCfg)
+	theirControl, theirVpnIpNet, theirUdpAddr, _ := newSimpleServer(cert.Version2, ca, caKey, "them", "10.128.0.3/24", peerCfg)
+
+	r := router.NewR(t, lhControl, myControl, theirControl)
+	defer r.RenderFlow()
+	defer func() {
+		lhControl.Stop()
+		myControl.Stop()
+		theirControl.Stop()
+	}()
+
+	lhControl.Start()
+	myControl.Start()
+	theirControl.Start()
+	r.RouteFor(time.Millisecond * 500)
+
+	myControl.InjectLightHouseAddr(theirVpnIpNet[0].Addr(), theirUdpAddr)
+	theirControl.InjectLightHouseAddr(myVpnIpNet[0].Addr(), myUdpAddr)
+
+	myControl.InjectTunPacket(BuildTunUDPPacket(theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("establish")))
+	r.RouteFor(time.Second)
+	if myControl.GetHostInfoByVpnAddr(theirVpnIpNet[0].Addr(), false) == nil {
+		t.Fatal("failed to establish the tunnel we are measuring")
+	}
+	r.RouteFor(time.Millisecond * 500)
+
+	// From here the peer's NAT has no state for us, everything we send it disappears
+	start := time.Now()
+	blackholed := 0
+	var recovered time.Duration
+
+	if rebind {
+		myControl.RebindUDPServer()
+	}
+
+	// Keep the tun busy the way someone retrying a stalled connection would
+	stop := make(chan struct{})
+	defer close(stop)
+	go func() {
+		tick := time.NewTicker(time.Millisecond * 200)
+		defer tick.Stop()
+		for {
+			select {
+			case <-stop:
+				return
+			case <-tick.C:
+				myControl.InjectTunPacket(BuildTunUDPPacket(
+					theirVpnIpNet[0].Addr(), 80, myVpnIpNet[0].Addr(), 80, []byte("retry")))
+			}
+		}
+	}()
+
+	r.RouteForAllExitFuncOrTimeout(time.Second*30, func(p *udp.Packet, c *nebula.Control) router.ExitType {
+		if c == theirControl && p.From == myControl.GetUDPAddr() {
+			blackholed++
+			return router.Drop
+		}
+
+		// The peer reaching us directly is the moment its NAT opened, whether that is a punch or a handshake
+		if c == myControl && p.From == theirUdpAddr {
+			recovered = time.Since(start)
+			return router.RouteAndExit
+		}
+
+		return router.KeepRouting
+	})
+
+	if recovered == 0 {
+		t.Fatalf("no recovery within 30s (%d packets blackholed)", blackholed)
+	}
+	return recovered, blackholed
+}

e2e/router/router.go

@@ -6,11 +6,13 @@ package router
 import (
 	"context"
 	"fmt"
+	"maps"
 	"net/netip"
 	"os"
 	"path/filepath"
 	"reflect"
 	"regexp"
+	"slices"
 	"sort"
 	"sync"
 	"sync/atomic"
@@ -22,7 +24,6 @@ import (
 	"github.com/slackhq/nebula"
 	"github.com/slackhq/nebula/header"
 	"github.com/slackhq/nebula/udp"
-	"golang.org/x/exp/maps"
 )
 
 // outNatKey is the (from, to) pair used by outNat. Comparable struct, so it works as a map key without the
@@ -114,6 +115,28 @@ type packet struct {
 	packet *udp.Packet
 	tun    bool // a packet pulled off a tun device
 	rx     bool // the packet was received by a udp device
+
+	// h is the nebula header, parsed once when the packet is recorded. parseErr says why there isn't one, which
+	// the flow log reports rather than hiding. Punchy sends a single byte, so an unparseable packet is normal.
+	h        header.H
+	parseErr error
+}
+
+// fromAddr and toAddr are the addresses this packet actually travelled between. Reading them off the control
+// instead would misreport the whole history once a test moves a node. Tun packets are synthesized without
+// addresses, so they fall back to the control.
+func (p *packet) fromAddr() netip.AddrPort {
+	if p.tun || !p.packet.From.IsValid() {
+		return p.from.GetUDPAddr()
+	}
+	return p.packet.From
+}
+
+func (p *packet) toAddr() netip.AddrPort {
+	if p.tun || !p.packet.To.IsValid() {
+		return p.to.GetUDPAddr()
+	}
+	return p.packet.To
 }
 
 func (p *packet) WasReceived() {
@@ -131,6 +154,9 @@ const (
 	ExitNow ExitType = 1
 	// RouteAndExit routes this packet and exits immediately afterwards
 	RouteAndExit ExitType = 2
+	// Drop discards this packet without delivering it and keeps routing. Use it to simulate a blackhole, such as
+	// a restrictive NAT refusing traffic from an address it has not seen.
+	Drop ExitType = 3
 )
 
 type ExitFunc func(packet *udp.Packet, receiver *nebula.Control) ExitType
@@ -141,7 +167,9 @@ type ExitFunc func(packet *udp.Packet, receiver *nebula.Control) ExitType
 func NewR(t testing.TB, controls ...*nebula.Control) *R {
 	ctx, cancel := context.WithCancel(context.Background())
 
-	if err := os.MkdirAll("mermaid", 0755); err != nil {
+	// t.Name() contains a slash for subtests, so the flow log can land in a nested directory
+	fn := filepath.Join("mermaid", fmt.Sprintf("%s.md", t.Name()))
+	if err := os.MkdirAll(filepath.Dir(fn), 0755); err != nil {
 		panic(err)
 	}
 
@@ -152,7 +180,7 @@ func NewR(t testing.TB, controls ...*nebula.Control) *R {
 		outNat:       make(map[outNatKey]netip.AddrPort),
 		flow:         []flowEntry{},
 		ignoreFlows:  []ignoreFlow{},
-		fn:           filepath.Join("mermaid", fmt.Sprintf("%s.md", t.Name())),
+		fn:           fn,
 		t:            t,
 		cancelRender: cancel,
 	}
@@ -249,7 +277,7 @@ func (r *R) renderFlow() {
 			continue
 		}
 
-		addr := e.packet.from.GetUDPAddr()
+		addr := e.packet.fromAddr()
 		if _, ok := participants[addr]; ok {
 			continue
 		}
@@ -268,7 +296,6 @@ func (r *R) renderFlow() {
 	}
 
 	// Print packets
-	h := &header.H{}
 	for _, e := range r.flow {
 		if e.packet == nil {
 			//fmt.Fprintf(f, "    note over %s: %s\n", strings.Join(participantsVals, ", "), e.note)
@@ -280,21 +307,22 @@ func (r *R) renderFlow() {
 			fmt.Fprintln(f, r.formatUdpPacket(p))
 
 		} else {
-			if err := h.Parse(p.packet.Data); err != nil {
-				panic(err)
-			}
-
 			line := "--x"
 			if p.rx {
 				line = "->>"
 			}
 
-			fmt.Fprintf(f,
-				"    %s%s%s: %s(%s), index %v, counter: %v\n",
-				normalizeName(p.from.GetUDPAddr().String()),
+			detail := fmt.Sprintf("%s(%s), index %v, counter: %v",
+				p.h.TypeName(), p.h.SubTypeName(), p.h.RemoteIndex, p.h.MessageCounter)
+			if p.parseErr != nil {
+				detail = fmt.Sprintf("unparsed, %v (%d bytes)", p.parseErr, len(p.packet.Data))
+			}
+
+			fmt.Fprintf(f, "    %s%s%s: %s\n",
+				normalizeName(p.fromAddr().String()),
 				line,
-				normalizeName(p.to.GetUDPAddr().String()),
-				h.TypeName(), h.SubTypeName(), h.RemoteIndex, h.MessageCounter,
+				normalizeName(p.toAddr().String()),
+				detail,
 			)
 		}
 	}
@@ -347,7 +375,7 @@ func (r *R) RenderHostmaps(title string, controls ...*nebula.Control) {
 }
 
 func (r *R) renderHostmaps(title string) {
-	c := maps.Values(r.controls)
+	c := slices.AppendSeq(make([]*nebula.Control, 0, len(r.controls)), maps.Values(r.controls))
 	sort.SliceStable(c, func(i, j int) bool {
 		return c[i].GetVpnAddrs()[0].Compare(c[j].GetVpnAddrs()[0]) > 0
 	})
@@ -408,29 +436,34 @@ func (r *R) unlockedInjectFlow(from, to *nebula.Control, p *udp.Packet, tun bool
 
 	r.renderHostmaps(fmt.Sprintf("Packet %v", len(r.flow)))
 
-	if len(r.ignoreFlows) > 0 {
-		var h header.H
-		err := h.Parse(p.Data)
-		if err != nil {
-			panic(err)
-		}
+	var h header.H
+	var parseErr error
+	if !tun {
+		parseErr = h.Parse(p.Data)
+	}
 
-		for _, i := range r.ignoreFlows {
-			if !tun {
-				if i.messageType == h.Type && i.subType == h.Subtype {
-					return nil
-				}
-			} else if i.tun.HasValue && i.tun.IsTrue {
+	// Decide before copying, the copy comes from a freelist and an ignored packet would never be released
+	for _, i := range r.ignoreFlows {
+		if tun {
+			if i.tun.HasValue && i.tun.IsTrue {
 				return nil
 			}
+			continue
+		}
+
+		// A packet we could not parse has no type to match against, so no rule can ignore it
+		if parseErr == nil && i.messageType == h.Type && i.subType == h.Subtype {
+			return nil
 		}
 	}
 
 	fp := &packet{
-		from:   from,
-		to:     to,
-		packet: p.Copy(),
-		tun:    tun,
+		from:     from,
+		to:       to,
+		packet:   p.Copy(),
+		tun:      tun,
+		h:        h,
+		parseErr: parseErr,
 	}
 
 	r.flow = append(r.flow, flowEntry{packet: fp})
@@ -660,6 +693,10 @@ func (r *R) RouteExitFunc(sender *nebula.Control, whatDo ExitFunc) {
 			p.Release()
 			return
 
+		case Drop:
+			// Record it so the flow log shows the attempt, but never hand it to the receiver
+			r.unlockedInjectFlow(sender, receiver, p, false)
+
 		case KeepRouting:
 			fp := r.unlockedInjectFlow(sender, receiver, p, false)
 			receiver.InjectUDPPacket(p)
@@ -690,6 +727,85 @@ func (r *R) RouteUntilAfterMsgType(sender *nebula.Control, msgType header.Messag
 	})
 }
 
+// RouteFor routes everything that shows up for the given duration and then returns. Use it to let a test settle
+// deterministically rather than sleeping and hoping: a single FlushAll races a completing handshake, which queues
+// more packets right behind it.
+func (r *R) RouteFor(d time.Duration) {
+	r.RouteForAllExitFuncOrTimeout(d, func(*udp.Packet, *nebula.Control) ExitType {
+		return KeepRouting
+	})
+}
+
+// RouteForAllExitFuncOrTimeout is RouteForAllExitFunc with a deadline, reporting whether whatDo asked to exit
+// before time ran out. The unbounded version blocks forever on a quiet network, so this is what a test needs to
+// assert that something does NOT happen, or to route for a fixed settling period.
+func (r *R) RouteForAllExitFuncOrTimeout(timeout time.Duration, whatDo ExitFunc) bool {
+	sc := make([]reflect.SelectCase, 0, len(r.controls)+1)
+	cm := make([]*nebula.Control, 0, len(r.controls))
+
+	for _, c := range r.controls {
+		sc = append(sc, reflect.SelectCase{
+			Dir:  reflect.SelectRecv,
+			Chan: reflect.ValueOf(c.GetUDPTxChan()),
+			Send: reflect.Value{},
+		})
+		cm = append(cm, c)
+	}
+
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+	sc = append(sc, reflect.SelectCase{
+		Dir:  reflect.SelectRecv,
+		Chan: reflect.ValueOf(timer.C),
+		Send: reflect.Value{},
+	})
+
+	for {
+		x, rx, _ := reflect.Select(sc)
+		if x == len(cm) {
+			return false
+		}
+
+		r.Lock()
+		p := rx.Interface().(*udp.Packet)
+		receiver := r.getControl(cm[x].GetUDPAddr(), p.To, p)
+		if receiver == nil {
+			r.Unlock()
+			panic("Can't RouteForAllExitFuncOrTimeout for host: " + p.To.String())
+		}
+
+		e := whatDo(p, receiver)
+		switch e {
+		case ExitNow:
+			r.Unlock()
+			p.Release()
+			return true
+
+		case RouteAndExit:
+			fp := r.unlockedInjectFlow(cm[x], receiver, p, false)
+			receiver.InjectUDPPacket(p)
+			fp.WasReceived()
+			r.Unlock()
+			p.Release()
+			return true
+
+		case Drop:
+			// Record it so the flow log shows the attempt, but never hand it to the receiver
+			r.unlockedInjectFlow(cm[x], receiver, p, false)
+
+		case KeepRouting:
+			fp := r.unlockedInjectFlow(cm[x], receiver, p, false)
+			receiver.InjectUDPPacket(p)
+			fp.WasReceived()
+
+		default:
+			panic(fmt.Sprintf("Unknown exitFunc return: %v", e))
+		}
+		r.Unlock()
+		p.Release()
+	}
+}
+
 func (r *R) RouteForAllUntilAfterMsgTypeTo(receiver *nebula.Control, msgType header.MessageType, subType header.MessageSubType) {
 	h := &header.H{}
 	r.RouteForAllExitFunc(func(p *udp.Packet, r *nebula.Control) ExitType {
@@ -782,6 +898,10 @@ func (r *R) RouteForAllExitFunc(whatDo ExitFunc) {
 			p.Release()
 			return
 
+		case Drop:
+			// Record it so the flow log shows the attempt, but never hand it to the receiver
+			r.unlockedInjectFlow(cm[x], receiver, p, false)
+
 		case KeepRouting:
 			fp := r.unlockedInjectFlow(cm[x], receiver, p, false)
 			receiver.InjectUDPPacket(p)

e2e/tunnels_test.go

@@ -43,8 +43,8 @@ func TestDropInactiveTunnels(t *testing.T) {
 	r.Log("Go inactive and wait for the tunnels to get dropped")
 	waitStart := time.Now()
 	for {
-		myIndexes := len(myControl.GetHostmap().Indexes)
-		theirIndexes := len(theirControl.GetHostmap().Indexes)
+		myIndexes := myControl.GetHostmapIndexCount()
+		theirIndexes := theirControl.GetHostmapIndexCount()
 		if myIndexes == 0 && theirIndexes == 0 {
 			break
 		}
@@ -493,8 +493,8 @@ func TestCloseTunnelAuthenticated(t *testing.T) {
 
 	waitStart := time.Now()
 	for {
-		myIndexes := len(myControl.GetHostmap().Indexes)
-		theirIndexes := len(theirControl.GetHostmap().Indexes)
+		myIndexes := myControl.GetHostmapIndexCount()
+		theirIndexes := theirControl.GetHostmapIndexCount()
 		if myIndexes == 0 && theirIndexes == 0 {
 			break
 		}
@@ -548,8 +548,8 @@ func TestCloseTunnelAuthenticated(t *testing.T) {
 	r.Log("Injected bogus close tunnel. Let's see!")
 	waitStart = time.Now()
 	for {
-		myIndexes := len(myControl.GetHostmap().Indexes)
-		theirIndexes := len(theirControl.GetHostmap().Indexes)
+		myIndexes := myControl.GetHostmapIndexCount()
+		theirIndexes := theirControl.GetHostmapIndexCount()
 		if myIndexes == 0 {
 			t.Fatal("myIndexes should not be 0")
 		}

examples/config.yml

@@ -131,6 +131,9 @@ listen:
   port: 4242
   # Sets the max number of packets to pull from the kernel for each syscall (under systems that support recvmmsg)
   # default is 64, does not support reload
+  # Note: on Linux with UDP GRO (kernel 5.10+), each receive slot is sized for a full 64KiB coalesced
+  # superpacket, so the receive scratch is batch * 64KiB per listening socket (~4MiB per routine at the
+  # default of 64). Lower this to trade peak per-syscall throughput for memory on constrained hosts.
   #batch: 64
   # Configure socket buffers for the udp side (outside), leave unset to use the system defaults. Values will be doubled by the kernel
   # Default is net.core.rmem_default and net.core.wmem_default (/proc/sys/net/core/rmem_default and /proc/sys/net/core/rmem_default)
@@ -146,6 +149,14 @@ listen:
   # Default true; set to false to leave WDF in charge of inbound decisions on the listener port. Not reloadable.
   #windows_bypass_wdf: true
 
+  # On macOS only
+  # macOS scopes the udp socket to the interface it was created on, so moving between networks (wifi to wired,
+  # office to home) leaves Nebula sending out an interface that no longer has a route. When true, Nebula watches
+  # the routing socket and rebinds the listener once the change settles.
+  # iOS does not use this, the host app drives the same rebind itself.
+  # Default true. Not reloadable.
+  #rebind_on_network_change: true
+
   # By default, Nebula replies to packets it has no tunnel for with a "recv_error" packet. This packet helps speed up reconnection
   # in the case that Nebula on either side did not shut down cleanly. This response can be abused as a way to discover if Nebula is running
   # on a host though. This option lets you configure if you want to send "recv_error" packets always, never, or only to private network remotes.
@@ -161,14 +172,61 @@ listen:
   # allowing for more precise routing decisions based on the packet tags. Default is 0 meaning no mark is set.
   # This setting is reloadable.
   #so_mark: 0
+  # the udp_offloads setting controls if Nebula will attempt to enable GSO and GRO for its UDP socket(s). Linux only, not reloadable.
+  # udp_offloads: false
 
 # Routines is the number of thread pairs to run that consume from the tun and UDP queues.
 # Currently, this defaults to 1 which means we have 1 tun queue reader and 1
 # UDP queue reader. Setting this above one will set IFF_MULTI_QUEUE on the tun
 # device and SO_REUSEPORT on the UDP socket to allow multiple queues.
+# With multiport enabled this is the number of routines *per port*, so the total
+# is routines * multiport.ports.
 # This option is only supported on Linux.
 #routines: 1
 
+# EXPERIMENTAL: multiport lanes give each pair of hosts multiple underlay UDP
+# flows so overlay traffic is no longer bottlenecked by a single 5-tuple
+# (one ECMP path, one NIC RSS queue, one per-flow policer). Instead of every
+# socket sharing listen.port, multiport.ports consecutive ports are bound and
+# each gets its own group of `routines` sockets sharing it via SO_REUSEPORT, so
+# no port (the base port above all, which carries every handshake and every
+# vanilla peer) depends on a single core. One extra tunnel ("lane") per port is
+# negotiated with capable peers: lane i handshakes from local port listen.port+i
+# to the peer's advertised base+((i + pair_offset) mod peer_ports), where
+# pair_offset is a per-pair hash that spreads many small peers across a big
+# peer's whole port range.
+# Each lane is a full Noise session with its own
+# keys, nonce counter and replay window, so flows taking different paths
+# never fight over shared replay state.
+#
+# Peers negotiate lanes in the handshake; vanilla peers get a single normal
+# tunnel. All control traffic (handshakes, lighthouse, punching, relays) and
+# the data fallback stay on the base tunnel/port. Lanes are built lazily: a
+# lane is only established once a routine actually has traffic for that peer
+# and no lane to carry it, so a peer you exchange a trickle with costs one
+# tunnel regardless of how many routines are configured. Established lanes
+# are kept alive with their own keepalives, and traffic falls back to the base
+# tunnel while a lane is down or not yet up.
+#
+# Requirements: multiport.ports > 1, Linux, and the port range
+# [listen.port, listen.port+multiport.ports-1] reachable through firewalls on
+# both sides. A lane whose port is unreachable stays down and its traffic rides
+# the base tunnel. With listen.port 0 the base port is dynamic and the next
+# ports-1 ports above it are claimed. Degrades to a single port when the
+# requirements don't hold. Not reloadable.
+#multiport:
+  #enabled: true
+  # How many consecutive UDP ports to bind, starting at listen.port. Must be
+  # greater than 1 for multiport to do anything; there is no default, since
+  # each port costs a full set of `routines` threads and sockets. Capped at 256
+  # (the lane header limit). 4-8 is plenty to escape a single ECMP path.
+  #ports: 0
+  # How many lanes to run, counting the base tunnel as lane 0. 0 (default)
+  # means one per bound port. Lowering this sends on a subset of the range,
+  # which bounds how many extra tunnels each peer pair maintains (useful on a
+  # big server with many peers); the ports are bound and read either way.
+  #lanes: 0
+
 punchy:
   # Continues to punch inbound/outbound at a regular interval to avoid expiration of firewall nat mappings
   # This setting is reloadable.
@@ -254,6 +312,33 @@ tun:
   # Default MTU for every packet, safe setting is (and the default) 1300 for internet based traffic
   mtu: 1300
 
+  # the use_offloads setting controls if Nebula will attempt to enable GSO and GRO for the tun device. Linux only, not reloadable.
+  #use_offloads: false
+
+  # Linux only. pin_threads pins each tun reader/encrypt OS thread to a single CPU. This keeps every goroutine's
+  # batched sends flowing through one XPS-selected NIC TX ring, so packets within a flow stay ordered on the wire
+  # instead of being sprayed across multiple TX rings and reordered. Not reloadable. Coerced to false if routines <= 1.
+  #pin_threads: true
+
+  # pin_threads_key helps the CPU-auto-selector shuffle which CPUs are chosen for pinning.
+  # Valid options are "pid" or "port". Use "port" if you want Nebula to choose the same cores every time, which is nice for benchmarking.
+  # Linux only, not reloadable.
+  #pin_threads_key: "pid"
+
+  # Linux only. cpu_affinity overrides which CPUs the tun reader threads pin to: a list of CPU IDs, one per routine
+  # (see the top-level `routines` setting). Lists shorter than `routines` are modulo-cycled across the queues; extra
+  # entries are ignored. IDs must be within the process's allowed CPU set, so this respects taskset / cgroup cpusets;
+  # a non-integer or not-allowed entry disables the override, leaving the default pin selection described below.
+  # Only meaningful while pin_threads is true. Not reloadable.
+  # When unset (or rejected), the default spread prefers performance cores on heterogeneous CPUs (ARM big.LITTLE,
+  # Intel P/E hybrids, AMD compact cores), keeps all readers on one NUMA node and on distinct physical cores when the
+  # topology allows (SMT siblings last), leaves CPU 0's physical core as a last resort, and rotates its starting
+  # point per instance (keyed by the bound UDP port) so co-located nebulas don't stack their readers onto the
+  # same cores.
+  #cpu_affinity:
+  #  - 2
+  #  - 4
+
   # Route based MTU overrides, you have known vpn ip paths that can support larger MTUs you can increase/decrease them here
   routes:
     #- mtu: 8800

examples/service_scripts/nebula.service

@@ -8,6 +8,15 @@ Before=sshd.service
 Type=notify
 NotifyAccess=main
 SyslogIdentifier=nebula
+
+# Uncomment to run as an unprivileged user with only CAP_NET_ADMIN. Requires a
+# nebula user that owns the config directory. Add CAP_NET_BIND_SERVICE to both
+# lines if any listener (lighthouse DNS, listen.port, stats, sshd) binds <1024.
+#User=nebula
+#Group=nebula
+#CapabilityBoundingSet=CAP_NET_ADMIN
+#AmbientCapabilities=CAP_NET_ADMIN
+
 ExecReload=/bin/kill -HUP $MAINPID
 ExecStart=/usr/local/bin/nebula -config /etc/nebula/config.yml
 Restart=always

firewall.go

@@ -21,6 +21,7 @@ import (
 	"github.com/slackhq/nebula/cert"
 	"github.com/slackhq/nebula/config"
 	"github.com/slackhq/nebula/firewall"
+	"github.com/slackhq/nebula/iputil"
 )
 
 type FirewallInterface interface {
@@ -44,8 +45,8 @@ type Firewall struct {
 	InRules  *FirewallTable
 	OutRules *FirewallTable
 
-	InSendReject  bool
-	OutSendReject bool
+	InboundSendReject  bool
+	OutboundSendReject bool
 
 	//TODO: we should have many more options for TCP, an option for ICMP, and mimic the kernel a bit better
 	// https://www.kernel.org/doc/Documentation/networking/nf_conntrack-sysctl.txt
@@ -216,23 +217,23 @@ func NewFirewallFromConfig(l *slog.Logger, cs *CertState, c *config.C) (*Firewal
 	inboundAction := c.GetString("firewall.inbound_action", "drop")
 	switch inboundAction {
 	case "reject":
-		fw.InSendReject = true
+		fw.InboundSendReject = true
 	case "drop":
-		fw.InSendReject = false
+		fw.InboundSendReject = false
 	default:
 		l.Warn("invalid firewall.inbound_action, defaulting to `drop`", "action", inboundAction)
-		fw.InSendReject = false
+		fw.InboundSendReject = false
 	}
 
 	outboundAction := c.GetString("firewall.outbound_action", "drop")
 	switch outboundAction {
 	case "reject":
-		fw.OutSendReject = true
+		fw.OutboundSendReject = true
 	case "drop":
-		fw.OutSendReject = false
+		fw.OutboundSendReject = false
 	default:
 		l.Warn("invalid firewall.outbound_action, defaulting to `drop`", "action", outboundAction)
-		fw.OutSendReject = false
+		fw.OutboundSendReject = false
 	}
 
 	err := AddFirewallRulesFromConfig(l, false, c, fw)
@@ -262,11 +263,11 @@ func (f *Firewall) AddRule(incoming bool, proto uint8, startPort int32, endPort
 	}
 
 	switch proto {
-	case firewall.ProtoTCP:
+	case iputil.IPProtocolTCP:
 		fp = ft.TCP
-	case firewall.ProtoUDP:
+	case iputil.IPProtocolUDP:
 		fp = ft.UDP
-	case firewall.ProtoICMP, firewall.ProtoICMPv6:
+	case iputil.IPProtocolICMP, iputil.IPProtocolICMPv6:
 		//ICMP traffic doesn't have ports, so we always coerce to "any", even if a value is provided
 		if startPort != firewall.PortAny {
 			f.l.Warn("ignoring port specification for ICMP firewall rule", "startPort", startPort)
@@ -364,13 +365,13 @@ func AddFirewallRulesFromConfig(l *slog.Logger, inbound bool, c *config.C, fw Fi
 			proto = firewall.ProtoAny
 			startPort, endPort, err = parsePort(sPort)
 		case "tcp":
-			proto = firewall.ProtoTCP
+			proto = iputil.IPProtocolTCP
 			startPort, endPort, err = parsePort(sPort)
 		case "udp":
-			proto = firewall.ProtoUDP
+			proto = iputil.IPProtocolUDP
 			startPort, endPort, err = parsePort(sPort)
 		case "icmp":
-			proto = firewall.ProtoICMP
+			proto = iputil.IPProtocolICMP
 			startPort = firewall.PortAny
 			endPort = firewall.PortAny
 			if sPort != "" {
@@ -560,9 +561,9 @@ func (f *Firewall) inConns(fp firewall.Packet, h *HostInfo, caPool *cert.CAPool,
 	}
 
 	switch fp.Protocol {
-	case firewall.ProtoTCP:
+	case iputil.IPProtocolTCP:
 		c.Expires = time.Now().Add(f.TCPTimeout)
-	case firewall.ProtoUDP:
+	case iputil.IPProtocolUDP:
 		c.Expires = time.Now().Add(f.UDPTimeout)
 	default:
 		c.Expires = time.Now().Add(f.DefaultTimeout)
@@ -582,9 +583,9 @@ func (f *Firewall) addConn(fp firewall.Packet, incoming bool) {
 	c := &conn{}
 
 	switch fp.Protocol {
-	case firewall.ProtoTCP:
+	case iputil.IPProtocolTCP:
 		timeout = f.TCPTimeout
-	case firewall.ProtoUDP:
+	case iputil.IPProtocolUDP:
 		timeout = f.UDPTimeout
 	default:
 		timeout = f.DefaultTimeout
@@ -635,15 +636,15 @@ func (ft *FirewallTable) match(p firewall.Packet, incoming bool, c *cert.CachedC
 	}
 
 	switch p.Protocol {
-	case firewall.ProtoTCP:
+	case iputil.IPProtocolTCP:
 		if ft.TCP.match(p, incoming, c, caPool) {
 			return true
 		}
-	case firewall.ProtoUDP:
+	case iputil.IPProtocolUDP:
 		if ft.UDP.match(p, incoming, c, caPool) {
 			return true
 		}
-	case firewall.ProtoICMP, firewall.ProtoICMPv6:
+	case iputil.IPProtocolICMP, iputil.IPProtocolICMPv6:
 		if ft.ICMP.match(p, incoming, c, caPool) {
 			return true
 		}
@@ -680,7 +681,7 @@ func (fp firewallPort) match(p firewall.Packet, incoming bool, c *cert.CachedCer
 	}
 
 	// this branch is here to catch traffic from FirewallTable.Any.match and FirewallTable.ICMP.match
-	if p.Protocol == firewall.ProtoICMP || p.Protocol == firewall.ProtoICMPv6 {
+	if p.Protocol == iputil.IPProtocolICMP || p.Protocol == iputil.IPProtocolICMPv6 {
 		// port numbers are re-used for connection tracking of ICMP,
 		// but we don't want to actually filter on them.
 		return fp[firewall.PortAny].match(p, c, caPool)

firewall/cache.go

@@ -5,6 +5,8 @@ import (
 	"log/slog"
 	"sync/atomic"
 	"time"
+
+	"github.com/slackhq/nebula/logging"
 )
 
 // ConntrackCache is used as a local routine cache to know if a given flow
@@ -56,8 +58,8 @@ func (c *ConntrackCacheTicker) Get() ConntrackCache {
 	if tick := c.cacheTick.Load(); tick != c.cacheV {
 		c.cacheV = tick
 		if ll := len(c.cache); ll > 0 {
-			if c.l.Enabled(context.Background(), slog.LevelDebug) {
-				c.l.Debug("resetting conntrack cache", "len", ll)
+			if c.l.Enabled(context.Background(), logging.LevelTrace) {
+				c.l.Log(context.Background(), logging.LevelTrace, "resetting conntrack cache", "len", ll)
 			}
 			c.cache = make(ConntrackCache, ll)
 		}

firewall/cache_test.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/slackhq/nebula/logging"
 	"github.com/slackhq/nebula/test"
 	"github.com/stretchr/testify/assert"
 )
@@ -30,27 +31,27 @@ func newFixedTicker(t *testing.T, l *slog.Logger, cacheLen int) *ConntrackCacheT
 
 func TestConntrackCacheTicker_Get_TextFormat(t *testing.T) {
 	buf := &bytes.Buffer{}
-	l := test.NewLoggerWithOutputAndLevel(buf, slog.LevelDebug)
+	l := test.NewLoggerWithOutputAndLevel(buf, logging.LevelTrace)
 
 	c := newFixedTicker(t, l, 3)
 	c.Get()
 
-	assert.Equal(t, "level=DEBUG msg=\"resetting conntrack cache\" len=3\n", buf.String())
+	assert.Equal(t, "level=DEBUG-4 msg=\"resetting conntrack cache\" len=3\n", buf.String())
 }
 
 func TestConntrackCacheTicker_Get_JSONFormat(t *testing.T) {
 	buf := &bytes.Buffer{}
-	l := test.NewJSONLoggerWithOutput(buf, slog.LevelDebug)
+	l := test.NewJSONLoggerWithOutput(buf, logging.LevelTrace)
 
 	c := newFixedTicker(t, l, 2)
 	c.Get()
 
-	assert.JSONEq(t, `{"level":"DEBUG","msg":"resetting conntrack cache","len":2}`, strings.TrimSpace(buf.String()))
+	assert.JSONEq(t, `{"level":"DEBUG-4","msg":"resetting conntrack cache","len":2}`, strings.TrimSpace(buf.String()))
 }
 
-func TestConntrackCacheTicker_Get_QuietBelowDebug(t *testing.T) {
+func TestConntrackCacheTicker_Get_QuietBelowTrace(t *testing.T) {
 	buf := &bytes.Buffer{}
-	l := test.NewLoggerWithOutputAndLevel(buf, slog.LevelInfo)
+	l := test.NewLoggerWithOutputAndLevel(buf, slog.LevelDebug)
 
 	c := newFixedTicker(t, l, 5)
 	c.Get()
@@ -60,7 +61,7 @@ func TestConntrackCacheTicker_Get_QuietBelowDebug(t *testing.T) {
 
 func TestConntrackCacheTicker_Get_QuietWhenCacheEmpty(t *testing.T) {
 	buf := &bytes.Buffer{}
-	l := test.NewLoggerWithOutputAndLevel(buf, slog.LevelDebug)
+	l := test.NewLoggerWithOutputAndLevel(buf, logging.LevelTrace)
 
 	c := newFixedTicker(t, l, 0)
 	c.Get()

firewall/packet.go

@@ -4,17 +4,14 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/netip"
+
+	"github.com/slackhq/nebula/iputil"
 )
 
 type m = map[string]any
 
 const (
-	ProtoAny    = 0 // When we want to handle HOPOPT (0) we can change this, if ever
-	ProtoTCP    = 6
-	ProtoUDP    = 17
-	ProtoICMP   = 1
-	ProtoICMPv6 = 58
-
+	ProtoAny     = 0  // When we want to handle HOPOPT (0) we can change this, if ever
 	PortAny      = 0  // Special value for matching `port: any`
 	PortFragment = -1 // Special value for matching `port: fragment`
 )
@@ -45,13 +42,13 @@ func (fp *Packet) Copy() *Packet {
 func (fp Packet) MarshalJSON() ([]byte, error) {
 	var proto string
 	switch fp.Protocol {
-	case ProtoTCP:
+	case iputil.IPProtocolTCP:
 		proto = "tcp"
-	case ProtoICMP:
+	case iputil.IPProtocolICMP:
 		proto = "icmp"
-	case ProtoICMPv6:
+	case iputil.IPProtocolICMPv6:
 		proto = "icmpv6"
-	case ProtoUDP:
+	case iputil.IPProtocolUDP:
 		proto = "udp"
 	default:
 		proto = fmt.Sprintf("unknown %v", fp.Protocol)
@@ -65,3 +62,12 @@ func (fp Packet) MarshalJSON() ([]byte, error) {
 		"Fragment":   fp.Fragment,
 	})
 }
+
+// ParsedPacket is a Packet plus the parse byproducts the RX path reuses
+type ParsedPacket struct {
+	Packet
+	IPHdrLen int
+	// FragAny reports any fragmentation at all: MF flag or nonzero offset for IPv4, a fragment extension header for IPv6.
+	// Distinct from Packet.Fragment, which is true only for NON-FIRST fragments
+	FragAny bool
+}

firewall_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/slackhq/nebula/cert"
 	"github.com/slackhq/nebula/config"
 	"github.com/slackhq/nebula/firewall"
+	"github.com/slackhq/nebula/iputil"
 	"github.com/slackhq/nebula/test"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -72,20 +73,20 @@ func TestFirewall_AddRule(t *testing.T) {
 	ti6, err := netip.ParsePrefix("fd12::34/128")
 	require.NoError(t, err)
 
-	require.NoError(t, fw.AddRule(true, firewall.ProtoTCP, 1, 1, []string{}, "", "", "", "", ""))
+	require.NoError(t, fw.AddRule(true, iputil.IPProtocolTCP, 1, 1, []string{}, "", "", "", "", ""))
 	// An empty rule is any
 	assert.True(t, fw.InRules.TCP[1].Any.Any.Any)
 	assert.Empty(t, fw.InRules.TCP[1].Any.Groups)
 	assert.Empty(t, fw.InRules.TCP[1].Any.Hosts)
 
 	fw = NewFirewall(l, time.Second, time.Minute, time.Hour, c)
-	require.NoError(t, fw.AddRule(true, firewall.ProtoUDP, 1, 1, []string{"g1"}, "", "", "", "", ""))
+	require.NoError(t, fw.AddRule(true, iputil.IPProtocolUDP, 1, 1, []string{"g1"}, "", "", "", "", ""))
 	assert.Nil(t, fw.InRules.UDP[1].Any.Any)
 	assert.Contains(t, fw.InRules.UDP[1].Any.Groups[0].Groups, "g1")
 	assert.Empty(t, fw.InRules.UDP[1].Any.Hosts)
 
 	fw = NewFirewall(l, time.Second, time.Minute, time.Hour, c)
-	require.NoError(t, fw.AddRule(true, firewall.ProtoICMP, 1, 1, []string{}, "h1", "", "", "", ""))
+	require.NoError(t, fw.AddRule(true, iputil.IPProtocolICMP, 1, 1, []string{}, "h1", "", "", "", ""))
 	//no matter what port is given for icmp, it should end up as "any"
 	assert.Nil(t, fw.InRules.ICMP[firewall.PortAny].Any.Any)
 	assert.Empty(t, fw.InRules.ICMP[firewall.PortAny].Any.Groups)
@@ -116,11 +117,11 @@ func TestFirewall_AddRule(t *testing.T) {
 	assert.True(t, ok)
 
 	fw = NewFirewall(l, time.Second, time.Minute, time.Hour, c)
-	require.NoError(t, fw.AddRule(true, firewall.ProtoUDP, 1, 1, []string{"g1"}, "", "", "", "ca-name", ""))
+	require.NoError(t, fw.AddRule(true, iputil.IPProtocolUDP, 1, 1, []string{"g1"}, "", "", "", "ca-name", ""))
 	assert.Contains(t, fw.InRules.UDP[1].CANames, "ca-name")
 
 	fw = NewFirewall(l, time.Second, time.Minute, time.Hour, c)
-	require.NoError(t, fw.AddRule(true, firewall.ProtoUDP, 1, 1, []string{"g1"}, "", "", "", "", "ca-sha"))
+	require.NoError(t, fw.AddRule(true, iputil.IPProtocolUDP, 1, 1, []string{"g1"}, "", "", "", "", "ca-sha"))
 	assert.Contains(t, fw.InRules.UDP[1].CAShas, "ca-sha")
 
 	fw = NewFirewall(l, time.Second, time.Minute, time.Hour, c)
@@ -185,7 +186,7 @@ func TestFirewall_Drop(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("1.2.3.4"),
 		LocalPort:  10,
 		RemotePort: 90,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 
@@ -263,7 +264,7 @@ func TestFirewall_DropV6(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("fd12::34"),
 		LocalPort:  10,
 		RemotePort: 90,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 
@@ -350,7 +351,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			Certificate: &dummyCert{},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoUDP}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolUDP}, true, c, cp))
 		}
 	})
 
@@ -360,7 +361,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			Certificate: &dummyCert{},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 1}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 1}, true, c, cp))
 		}
 	})
 
@@ -370,7 +371,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 		}
 		ip := netip.MustParsePrefix("9.254.254.254/32")
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 100, LocalAddr: ip.Addr()}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 100, LocalAddr: ip.Addr()}, true, c, cp))
 		}
 	})
 	b.Run("pass proto, port, fail on local CIDRv6", func(b *testing.B) {
@@ -379,7 +380,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 		}
 		ip := netip.MustParsePrefix("fd99::99/128")
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 100, LocalAddr: ip.Addr()}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 100, LocalAddr: ip.Addr()}, true, c, cp))
 		}
 	})
 
@@ -392,7 +393,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"nope": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 10}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 10}, true, c, cp))
 		}
 	})
 	b.Run("pass proto, port, any local CIDRv6, fail all group, name, and cidr", func(b *testing.B) {
@@ -404,7 +405,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"nope": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 10}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 10}, true, c, cp))
 		}
 	})
 
@@ -417,7 +418,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"nope": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 100, LocalAddr: pfix.Addr()}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 100, LocalAddr: pfix.Addr()}, true, c, cp))
 		}
 	})
 	b.Run("pass proto, port, specific local CIDRv6, fail all group, name, and cidr", func(b *testing.B) {
@@ -429,7 +430,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"nope": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.False(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 100, LocalAddr: pfix6.Addr()}, true, c, cp))
+			assert.False(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 100, LocalAddr: pfix6.Addr()}, true, c, cp))
 		}
 	})
 
@@ -441,7 +442,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"good-group": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.True(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 10}, true, c, cp))
+			assert.True(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 10}, true, c, cp))
 		}
 	})
 
@@ -453,7 +454,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"good-group": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.True(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 100, LocalAddr: pfix.Addr()}, true, c, cp))
+			assert.True(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 100, LocalAddr: pfix.Addr()}, true, c, cp))
 		}
 	})
 	b.Run("pass on group on specific local cidr6", func(b *testing.B) {
@@ -464,7 +465,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"good-group": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			assert.True(b, ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 100, LocalAddr: pfix6.Addr()}, true, c, cp))
+			assert.True(b, ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 100, LocalAddr: pfix6.Addr()}, true, c, cp))
 		}
 	})
 
@@ -476,7 +477,7 @@ func BenchmarkFirewallTable_match(b *testing.B) {
 			InvertedGroups: map[string]struct{}{"nope": {}},
 		}
 		for n := 0; n < b.N; n++ {
-			ft.match(firewall.Packet{Protocol: firewall.ProtoTCP, LocalPort: 10}, true, c, cp)
+			ft.match(firewall.Packet{Protocol: iputil.IPProtocolTCP, LocalPort: 10}, true, c, cp)
 		}
 	})
 }
@@ -492,7 +493,7 @@ func TestFirewall_Drop2(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("1.2.3.4"),
 		LocalPort:  10,
 		RemotePort: 90,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 
@@ -550,7 +551,7 @@ func TestFirewall_Drop3(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("1.2.3.4"),
 		LocalPort:  1,
 		RemotePort: 1,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 
@@ -638,7 +639,7 @@ func TestFirewall_Drop3V6(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("fd12::34"),
 		LocalPort:  1,
 		RemotePort: 1,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 
@@ -675,7 +676,7 @@ func TestFirewall_DropConntrackReload(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("1.2.3.4"),
 		LocalPort:  10,
 		RemotePort: 90,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 	network := netip.MustParsePrefix("1.2.3.4/24")
@@ -758,13 +759,13 @@ func TestFirewall_ICMPPortBehavior(t *testing.T) {
 	templ := firewall.Packet{
 		LocalAddr:  netip.MustParseAddr("1.2.3.4"),
 		RemoteAddr: netip.MustParseAddr("1.2.3.4"),
-		Protocol:   firewall.ProtoICMP,
+		Protocol:   iputil.IPProtocolICMP,
 		Fragment:   false,
 	}
 
 	t.Run("ICMP allowed", func(t *testing.T) {
 		fw := NewFirewall(l, time.Second, time.Minute, time.Hour, c.Certificate)
-		require.NoError(t, fw.AddRule(true, firewall.ProtoICMP, 0, 0, []string{"any"}, "", "", "", "", ""))
+		require.NoError(t, fw.AddRule(true, iputil.IPProtocolICMP, 0, 0, []string{"any"}, "", "", "", "", ""))
 		t.Run("zero ports", func(t *testing.T) {
 			p := templ.Copy()
 			p.LocalPort = 0
@@ -910,7 +911,7 @@ func TestFirewall_DropIPSpoofing(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("192.0.2.3"),
 		LocalPort:  1,
 		RemotePort: 1,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 	assert.Equal(t, fw.Drop(p, true, &h1, cp, nil), ErrInvalidRemoteIP)
@@ -961,7 +962,7 @@ func TestFirewall_ConntrackSourceSpoofingAcrossPeers(t *testing.T) {
 		RemoteAddr: netip.MustParseAddr("192.0.2.2"),
 		LocalPort:  443,
 		RemotePort: 55000,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 	}
 
 	require.NoError(t, fw.Drop(flow, true, &victimHI, cp, nil),
@@ -1031,7 +1032,7 @@ func BenchmarkFirewallDropConntrackHit(b *testing.B) {
 		RemoteAddr: netip.MustParseAddr("192.0.2.2"),
 		LocalPort:  443,
 		RemotePort: 55000,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 	}
 
 	cases := []struct {
@@ -1317,28 +1318,28 @@ func TestAddFirewallRulesFromConfig(t *testing.T) {
 	mf := &mockFirewall{}
 	conf.Settings["firewall"] = map[string]any{"outbound": []any{map[string]any{"port": "1", "proto": "tcp", "host": "a"}}}
 	require.NoError(t, AddFirewallRulesFromConfig(l, false, conf, mf))
-	assert.Equal(t, addRuleCall{incoming: false, proto: firewall.ProtoTCP, startPort: 1, endPort: 1, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
+	assert.Equal(t, addRuleCall{incoming: false, proto: iputil.IPProtocolTCP, startPort: 1, endPort: 1, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
 
 	// Test adding udp rule
 	conf = config.NewC(test.NewLogger())
 	mf = &mockFirewall{}
 	conf.Settings["firewall"] = map[string]any{"outbound": []any{map[string]any{"port": "1", "proto": "udp", "host": "a"}}}
 	require.NoError(t, AddFirewallRulesFromConfig(l, false, conf, mf))
-	assert.Equal(t, addRuleCall{incoming: false, proto: firewall.ProtoUDP, startPort: 1, endPort: 1, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
+	assert.Equal(t, addRuleCall{incoming: false, proto: iputil.IPProtocolUDP, startPort: 1, endPort: 1, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
 
 	// Test adding icmp rule
 	conf = config.NewC(test.NewLogger())
 	mf = &mockFirewall{}
 	conf.Settings["firewall"] = map[string]any{"outbound": []any{map[string]any{"port": "1", "proto": "icmp", "host": "a"}}}
 	require.NoError(t, AddFirewallRulesFromConfig(l, false, conf, mf))
-	assert.Equal(t, addRuleCall{incoming: false, proto: firewall.ProtoICMP, startPort: firewall.PortAny, endPort: firewall.PortAny, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
+	assert.Equal(t, addRuleCall{incoming: false, proto: iputil.IPProtocolICMP, startPort: firewall.PortAny, endPort: firewall.PortAny, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
 
 	// Test adding icmp rule no port
 	conf = config.NewC(test.NewLogger())
 	mf = &mockFirewall{}
 	conf.Settings["firewall"] = map[string]any{"outbound": []any{map[string]any{"proto": "icmp", "host": "a"}}}
 	require.NoError(t, AddFirewallRulesFromConfig(l, false, conf, mf))
-	assert.Equal(t, addRuleCall{incoming: false, proto: firewall.ProtoICMP, startPort: firewall.PortAny, endPort: firewall.PortAny, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
+	assert.Equal(t, addRuleCall{incoming: false, proto: iputil.IPProtocolICMP, startPort: firewall.PortAny, endPort: firewall.PortAny, groups: nil, host: "a", ip: "", localIp: ""}, mf.lastCall)
 
 	// Test adding any rule
 	conf = config.NewC(test.NewLogger())
@@ -1582,7 +1583,7 @@ func buildTestCase(setup testsetup, err error, theirPrefixes ...netip.Prefix) te
 		RemoteAddr: theirPrefixes[0].Addr(),
 		LocalPort:  10,
 		RemotePort: 90,
-		Protocol:   firewall.ProtoUDP,
+		Protocol:   iputil.IPProtocolUDP,
 		Fragment:   false,
 	}
 	return testcase{

go.mod

@@ -1,13 +1,12 @@
 module github.com/slackhq/nebula
 
-go 1.25.0
+go 1.26.0
 
 require (
 	dario.cat/mergo v1.0.2
 	filippo.io/bigmod v0.1.0
 	github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be
 	github.com/armon/go-radix v1.0.0
-	github.com/cyberdelia/go-metrics-graphite v0.0.0-20161219230853-39f87cc3b432
 	github.com/flynn/noise v1.1.0
 	github.com/gaissmai/bart v0.28.0
 	github.com/gogo/protobuf v1.3.2
@@ -16,20 +15,19 @@ require (
 	github.com/miekg/dns v1.1.72
 	github.com/miekg/pkcs11 v1.1.2
 	github.com/nbrownus/go-metrics-prometheus v0.0.0-20210712211119-974a6260965f
-	github.com/prometheus/client_golang v1.23.2
+	github.com/prometheus/client_golang v1.24.1
 	github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
 	github.com/stefanberger/go-pkcs11uri v0.0.0-20230803200340-78284954bff6
-	github.com/stretchr/testify v1.11.1
+	github.com/stretchr/testify v1.12.0
 	github.com/vishvananda/netlink v1.3.1
 	go.uber.org/goleak v1.3.0
-	go.yaml.in/yaml/v3 v3.0.4
-	golang.org/x/crypto v0.53.0
-	golang.org/x/exp v0.0.0-20230725093048-515e97ebf090
-	golang.org/x/net v0.56.0
-	golang.org/x/sync v0.21.0
-	golang.org/x/sys v0.46.0
-	golang.org/x/term v0.44.0
+	go.yaml.in/yaml/v3 v3.0.5
+	golang.org/x/crypto v0.54.0
+	golang.org/x/net v0.57.0
+	golang.org/x/sync v0.22.0
+	golang.org/x/sys v0.47.0
+	golang.org/x/term v0.45.0
 	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2
 	golang.zx2c4.com/wireguard v0.0.0-20230325221338-052af4a8072b
 	golang.zx2c4.com/wireguard/windows v1.0.1
@@ -41,15 +39,12 @@ require (
 require (
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
-	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/google/btree v1.1.2 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/client_model v0.6.2 // indirect
-	github.com/prometheus/common v0.66.1 // indirect
-	github.com/prometheus/procfs v0.16.1 // indirect
+	github.com/prometheus/common v0.70.1 // indirect
+	github.com/prometheus/procfs v0.21.1 // indirect
 	github.com/vishvananda/netns v0.0.5 // indirect
-	go.yaml.in/yaml/v2 v2.4.2 // indirect
 	golang.org/x/mod v0.36.0 // indirect
 	golang.org/x/time v0.5.0 // indirect
 	golang.org/x/tools v0.45.0 // indirect

go.sum

@@ -19,10 +19,7 @@ github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6r
 github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
-github.com/cyberdelia/go-metrics-graphite v0.0.0-20161219230853-39f87cc3b432 h1:M5QgkYacWj0Xs8MhpIK/5uwU02icXpEoSo9sM2aRCps=
-github.com/cyberdelia/go-metrics-graphite v0.0.0-20161219230853-39f87cc3b432/go.mod h1:xwIwAxMvYnVrGJPe2FKx5prTrnAjGOD8zvDOnxnrrkM=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/flynn/noise v1.1.0 h1:KjPQoQCEFdZDiP03phOvGi11+SVVhBG2wOWAorLsstg=
 github.com/flynn/noise v1.1.0/go.mod h1:xbMo+0i6+IGbYdJhF31t2eR1BIU0CYc12+BNAKwUTag=
@@ -70,15 +67,14 @@ github.com/kardianos/service v1.3.0 h1:/LGy+xPP2TM+GLTiCZ2di7cy0Jd/qrawlTUfqKYFd
 github.com/kardianos/service v1.3.0/go.mod h1:E4V9ufUuY82F7Ztlu1eN9VXWIQxg8NoLQlmFe0MtrXc=
 github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
-github.com/klauspost/compress v1.18.0 h1:c/Cqfb0r+Yi+JtIEq73FWXVkRonBlf0CRNYc8Zttxdo=
-github.com/klauspost/compress v1.18.0/go.mod h1:2Pp+KzxcywXVXMr50+X0Q/Lsb43OQHYWRCY2AiWywWQ=
+github.com/klauspost/compress v1.19.1 h1:VsB4HPswih7mmZ8WleSFQ75c/Ui1M4trX5oAsJnhSlk=
+github.com/klauspost/compress v1.19.1/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/konsorten/go-windows-terminal-sequences v1.0.3/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515/go.mod h1:+0opPa2QZZtGFBFZlji/RkVcI2GknAs/DXo4wKdlNEc=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
-github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
-github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
@@ -102,14 +98,13 @@ github.com/nbrownus/go-metrics-prometheus v0.0.0-20210712211119-974a6260965f/go.
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
-github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXPKyh/dDVn+NZz0KFw=
 github.com/prometheus/client_golang v1.0.0/go.mod h1:db9x61etRT2tGnBNRi70OPL5FsnadC4Ky3P0J6CfImo=
 github.com/prometheus/client_golang v1.7.1/go.mod h1:PY5Wy2awLA44sXw4AOSfFBetzPP4j5+D6mVACh+pe2M=
 github.com/prometheus/client_golang v1.11.0/go.mod h1:Z6t4BnS23TR94PD6BsDNk8yVqroYurpAkEiz0P2BEV0=
-github.com/prometheus/client_golang v1.23.2 h1:Je96obch5RDVy3FDMndoUsjAhG5Edi49h0RJWRi/o0o=
-github.com/prometheus/client_golang v1.23.2/go.mod h1:Tb1a6LWHB3/SPIzCoaDXI4I8UHKeFTEQ1YCr+0Gyqmg=
+github.com/prometheus/client_golang v1.24.1 h1:JnJkREXzWxUdCuPFpIWZiPispT9xVV59uiuyR2bPlnU=
+github.com/prometheus/client_golang v1.24.1/go.mod h1:F+oSRECHg4sse5ucfYpYDeIv/hu68Zo0uoHKetWnzcE=
 github.com/prometheus/client_model v0.0.0-20180712105110-5c3871d89910/go.mod h1:MbSGuTsp3dbXC40dX6PRTWyKYBIrTGTE9sqQNg2J8bo=
 github.com/prometheus/client_model v0.0.0-20190129233127-fd36f4220a90/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
 github.com/prometheus/client_model v0.2.0/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
@@ -118,18 +113,16 @@ github.com/prometheus/client_model v0.6.2/go.mod h1:y3m2F6Gdpfy6Ut/GBsUqTWZqCUvM
 github.com/prometheus/common v0.4.1/go.mod h1:TNfzLD0ON7rHzMJeJkieUDPYmFC7Snx/y86RQel1bk4=
 github.com/prometheus/common v0.10.0/go.mod h1:Tlit/dnDKsSWFlCLTWaA1cyBgKHSMdTB80sz/V91rCo=
 github.com/prometheus/common v0.26.0/go.mod h1:M7rCNAaPfAosfx8veZJCuw84e35h3Cfd9VFqTh1DIvc=
-github.com/prometheus/common v0.66.1 h1:h5E0h5/Y8niHc5DlaLlWLArTQI7tMrsfQjHV+d9ZoGs=
-github.com/prometheus/common v0.66.1/go.mod h1:gcaUsgf3KfRSwHY4dIMXLPV0K/Wg1oZ8+SbZk/HH/dA=
+github.com/prometheus/common v0.70.1 h1:1HvjP4D5oL3t8RsPlwxA9onvvStjtIHYE5XuuwOi/PY=
+github.com/prometheus/common v0.70.1/go.mod h1:VdFUQDMZK3VLkurFUVhia6uys/0suUp86TJz5qbJRhc=
 github.com/prometheus/procfs v0.0.0-20181005140218-185b4288413d/go.mod h1:c3At6R/oaqEKCNdg8wHV1ftS6bRYblBhIjjI8uT2IGk=
 github.com/prometheus/procfs v0.0.2/go.mod h1:TjEm7ze935MbeOT/UhFTIMYKhuLP4wbCsTZCD3I8kEA=
 github.com/prometheus/procfs v0.1.3/go.mod h1:lV6e/gmhEcM9IjHGsFOCxxuZ+z1YqCvr4OA4YeYWdaU=
 github.com/prometheus/procfs v0.6.0/go.mod h1:cz+aTbrPOrUb4q7XlbU9ygM+/jj0fzG6c1xBZuNvfVA=
-github.com/prometheus/procfs v0.16.1 h1:hZ15bTNuirocR6u0JZ6BAHHmwS1p8B4P6MRqxtzMyRg=
-github.com/prometheus/procfs v0.16.1/go.mod h1:teAbpZRB1iIAJYREa1LsoWUXykVXA1KlTmWl8x/U+Is=
+github.com/prometheus/procfs v0.21.1 h1:GljZCt+zSTS+NZq88cyQ1LjZ+RCHp3uVuabBWA5+OJI=
+github.com/prometheus/procfs v0.21.1/go.mod h1:aB55Cww9pdSJVHk0hUf0inxWyyjPogFIjmHKYgMKmtY=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 h1:N/ElC8H3+5XpJzTSTfLsJV/mx9Q9g7kxmchpfZyxgzM=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
-github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
-github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
 github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6MwdIuYE2rE=
 github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrfsX/uA88=
@@ -143,8 +136,8 @@ github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXf
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
-github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/stretchr/testify v1.12.0 h1:K6Mr6jO9JICuend/5xzTM03ydSV3vdNRYAdPSukj8uI=
+github.com/stretchr/testify v1.12.0/go.mod h1:bOYBZb5qJ00vPzWfIqBUZPaxK8jWiXc6d3ErP4Ca9Gw=
 github.com/vishvananda/netlink v1.3.1 h1:3AEMt62VKqz90r0tmNhog0r/PpWKmrEShJU0wJW6bV0=
 github.com/vishvananda/netlink v1.3.1/go.mod h1:ARtKouGSTGchR8aMwmkzC0qiNPrrWO5JS/XMVl45+b4=
 github.com/vishvananda/netns v0.0.5 h1:DfiHV+j8bA32MFM7bfEunvT8IAqQ/NzSJHtcmW5zdEY=
@@ -153,19 +146,17 @@ github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9de
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
-go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
-go.yaml.in/yaml/v2 v2.4.2/go.mod h1:081UH+NErpNdqlCXm3TtEran0rJZGxAYx9hb/ELlsPU=
-go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
-go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
+go.yaml.in/yaml/v2 v2.4.4 h1:tuyd0P+2Ont/d6e2rl3be67goVK4R6deVxCUX5vyPaQ=
+go.yaml.in/yaml/v2 v2.4.4/go.mod h1:gMZqIpDtDqOfM0uNfy0SkpRhvUryYH0Z6wdMYcacYXQ=
+go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
+go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20210322153248-0c34fe9e7dc2/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
-golang.org/x/crypto v0.53.0 h1:QZ4Muo8THX6CizN2vPPd5fBGHyogrdK9fG4wLPFUsto=
-golang.org/x/crypto v0.53.0/go.mod h1:DNLU434OwVakk9PzuwV8w62mAJpRJL3vsgcfp4Qnsio=
-golang.org/x/exp v0.0.0-20230725093048-515e97ebf090 h1:Di6/M8l0O2lCLc6VVRWhgCiApHV8MnQurBnFSHsQtNY=
-golang.org/x/exp v0.0.0-20230725093048-515e97ebf090/go.mod h1:FXUEEKJgO7OQYeo8N01OfiKP8RXMtf6e8aTskBGqWdc=
+golang.org/x/crypto v0.54.0 h1:YLIA59K4fiNzHzjnZt2tUJQjQtUWfWbeHBqKtk3eScw=
+golang.org/x/crypto v0.54.0/go.mod h1:KWL8ny2AZdGR2cWmzeHrp2azQPGogOv+HeQaVEXC2dk=
 golang.org/x/lint v0.0.0-20200302205851-738671d3881b/go.mod h1:3xt1FjdF8hUf6vQPIChWIBhFzV8gjjsPE/fR3IyQdNY=
 golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
@@ -182,8 +173,8 @@ golang.org/x/net v0.0.0-20200226121028-0de0cce0169b/go.mod h1:z5CRVTTTmAJ677TzLL
 golang.org/x/net v0.0.0-20200625001655-4c5254603344/go.mod h1:/O7V0waA8r7cgGh81Ro3o1hOxt32SMVPicZroKQ2sZA=
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
-golang.org/x/net v0.56.0 h1:Rw8j/hFzGvJUZwNBXnAtf5sVDVt+65SK2C7IxCxZt5o=
-golang.org/x/net v0.56.0/go.mod h1:D3Ku6r+V6JROoZK144D2XfMHFcMq/0zSfLelVTCFKec=
+golang.org/x/net v0.57.0 h1:K5+3DljvIuDG9/Jv9rvyMywYNFCQ9RSUY6OOTTkT+tE=
+golang.org/x/net v0.57.0/go.mod h1:KpXc8iv+r3XplLAG/f7Jsf9RPszJzdR0f58q9vGOuEU=
 golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -191,8 +182,8 @@ golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.21.0 h1:HLII4xRRTtCRkxYp4HNFF0Js/Og6q2i++KXbg0gHCwM=
-golang.org/x/sync v0.21.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sync v0.22.0 h1:SZjpbeLmrCk4xhRSZFNZW5gFUeCeFgjekvI/+gfScek=
+golang.org/x/sync v0.22.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
@@ -208,11 +199,11 @@ golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210603081109-ebe580a85c40/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.46.0 h1:noSf2Fq6F8DBgS+LysIkx7rIExoNHJsxOAtPp4rthXw=
-golang.org/x/sys v0.46.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
+golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/term v0.44.0 h1:0rLvDRCtNj0gZkyIXhCyOb2OAzEhLVqc4B+hrsBhrmc=
-golang.org/x/term v0.44.0/go.mod h1:7ze4MdzUzLXpSAoFP1H0bOI9aXDqveSvatT5vKcFh2Y=
+golang.org/x/term v0.45.0 h1:NwWyBmoJCbfTHpxrWoZ9C6/VxOf7ic219I8xZZFdrf0=
+golang.org/x/term v0.45.0/go.mod h1:9aqxs0blBcrm/n0L9QW0aRVD+ktan8ssZromtqJC43w=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=

graphite.go

@@ -0,0 +1,117 @@
+package nebula
+
+// This file is a trimmed, inlined copy of the graphite exporter from
+// github.com/cyberdelia/go-metrics-graphite, retaining only the Config type and
+// the Once entrypoint that Nebula uses. The upstream package has been
+// unmaintained for 10+ years, so it was vendored here to drop the dependency.
+// See https://github.com/slackhq/nebula/issues/1831.
+//
+// Copyright 2015 Timothée Peignier. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//  1. Redistributions of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//
+//  2. Redistributions in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/rcrowley/go-metrics"
+)
+
+// graphiteConfigExport provides a container with configuration parameters for
+// the Graphite exporter.
+type graphiteConfigExport struct {
+	Addr          *net.TCPAddr     // Network address to connect to
+	Registry      metrics.Registry // Registry to be exported
+	FlushInterval time.Duration    // Flush interval
+	DurationUnit  time.Duration    // Time conversion unit for durations
+	Prefix        string           // Prefix to be prepended to metric names
+	Percentiles   []float64        // Percentiles to export from timers and histograms
+}
+
+// graphiteOnce performs a single submission to Graphite, returning a non-nil
+// error on failed connections.
+func graphiteOnce(c graphiteConfigExport) error {
+	now := time.Now().Unix()
+	du := float64(c.DurationUnit)
+	flushSeconds := float64(c.FlushInterval) / float64(time.Second)
+	conn, err := net.DialTCP("tcp", nil, c.Addr)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	w := bufio.NewWriter(conn)
+	c.Registry.Each(func(name string, i any) {
+		switch metric := i.(type) {
+		case metrics.Counter:
+			count := metric.Count()
+			fmt.Fprintf(w, "%s.%s.count %d %d\n", c.Prefix, name, count, now)
+			fmt.Fprintf(w, "%s.%s.count_ps %.2f %d\n", c.Prefix, name, float64(count)/flushSeconds, now)
+		case metrics.Gauge:
+			fmt.Fprintf(w, "%s.%s.value %d %d\n", c.Prefix, name, metric.Value(), now)
+		case metrics.GaugeFloat64:
+			fmt.Fprintf(w, "%s.%s.value %f %d\n", c.Prefix, name, metric.Value(), now)
+		case metrics.Histogram:
+			h := metric.Snapshot()
+			ps := h.Percentiles(c.Percentiles)
+			fmt.Fprintf(w, "%s.%s.count %d %d\n", c.Prefix, name, h.Count(), now)
+			fmt.Fprintf(w, "%s.%s.min %d %d\n", c.Prefix, name, h.Min(), now)
+			fmt.Fprintf(w, "%s.%s.max %d %d\n", c.Prefix, name, h.Max(), now)
+			fmt.Fprintf(w, "%s.%s.mean %.2f %d\n", c.Prefix, name, h.Mean(), now)
+			fmt.Fprintf(w, "%s.%s.std-dev %.2f %d\n", c.Prefix, name, h.StdDev(), now)
+			for psIdx, psKey := range c.Percentiles {
+				key := strings.Replace(strconv.FormatFloat(psKey*100.0, 'f', -1, 64), ".", "", 1)
+				fmt.Fprintf(w, "%s.%s.%s-percentile %.2f %d\n", c.Prefix, name, key, ps[psIdx], now)
+			}
+		case metrics.Meter:
+			m := metric.Snapshot()
+			fmt.Fprintf(w, "%s.%s.count %d %d\n", c.Prefix, name, m.Count(), now)
+			fmt.Fprintf(w, "%s.%s.one-minute %.2f %d\n", c.Prefix, name, m.Rate1(), now)
+			fmt.Fprintf(w, "%s.%s.five-minute %.2f %d\n", c.Prefix, name, m.Rate5(), now)
+			fmt.Fprintf(w, "%s.%s.fifteen-minute %.2f %d\n", c.Prefix, name, m.Rate15(), now)
+			fmt.Fprintf(w, "%s.%s.mean %.2f %d\n", c.Prefix, name, m.RateMean(), now)
+		case metrics.Timer:
+			t := metric.Snapshot()
+			ps := t.Percentiles(c.Percentiles)
+			count := t.Count()
+			fmt.Fprintf(w, "%s.%s.count %d %d\n", c.Prefix, name, count, now)
+			fmt.Fprintf(w, "%s.%s.count_ps %.2f %d\n", c.Prefix, name, float64(count)/flushSeconds, now)
+			fmt.Fprintf(w, "%s.%s.min %d %d\n", c.Prefix, name, t.Min()/int64(du), now)
+			fmt.Fprintf(w, "%s.%s.max %d %d\n", c.Prefix, name, t.Max()/int64(du), now)
+			fmt.Fprintf(w, "%s.%s.mean %.2f %d\n", c.Prefix, name, t.Mean()/du, now)
+			fmt.Fprintf(w, "%s.%s.std-dev %.2f %d\n", c.Prefix, name, t.StdDev()/du, now)
+			for psIdx, psKey := range c.Percentiles {
+				key := strings.Replace(strconv.FormatFloat(psKey*100.0, 'f', -1, 64), ".", "", 1)
+				fmt.Fprintf(w, "%s.%s.%s-percentile %.2f %d\n", c.Prefix, name, key, ps[psIdx]/du, now)
+			}
+			fmt.Fprintf(w, "%s.%s.one-minute %.2f %d\n", c.Prefix, name, t.Rate1(), now)
+			fmt.Fprintf(w, "%s.%s.five-minute %.2f %d\n", c.Prefix, name, t.Rate5(), now)
+			fmt.Fprintf(w, "%s.%s.fifteen-minute %.2f %d\n", c.Prefix, name, t.Rate15(), now)
+			fmt.Fprintf(w, "%s.%s.mean-rate %.2f %d\n", c.Prefix, name, t.RateMean(), now)
+		}
+		w.Flush()
+	})
+	return nil
+}

handshake/handshake.proto

@@ -26,4 +26,18 @@ message NebulaHandshakeDetails {
   uint32 CertVersion = 8;
   // reserved for WIP multiport
   reserved 6, 7;
+  // Multiport lane negotiation. Absent on hosts without multiport enabled;
+  // vanilla nebula treats 9 and 10 as unknown fields and skips them.
+  LaneDetails InitiatorLanes = 9;
+  LaneDetails ResponderLanes = 10;
+}
+
+// LaneDetails advertises a host's multiport lane capability. On a base
+// handshake LaneIndex is 0 and PortCount/BasePort describe the sender's
+// consecutively bound UDP ports. On a lane handshake the initiator sets
+// LaneIndex to its (nonzero) lane number.
+message LaneDetails {
+  uint32 PortCount = 1;
+  uint32 BasePort = 2;
+  uint32 LaneIndex = 3;
 }

handshake/helpers_test.go

@@ -71,6 +71,7 @@ func newTestMachine(
 		cs.version, cs.getCredential,
 		verifier, func() (uint32, error) { return localIndex, nil },
 		initiator, header.HandshakeIXPSK0,
+		nil,
 	)
 	require.NoError(t, err)
 	return m

handshake/machine.go

@@ -39,6 +39,14 @@ type Result struct {
 	HandshakeTime uint64
 	MessageIndex  uint64 // number of messages exchanged during the handshake
 	Initiator     bool
+
+	// Multiport lane negotiation, from the peer's LaneDetails. All zero when
+	// the peer did not advertise (vanilla peer or multiport disabled).
+	// PeerTxLanes is how many lanes the peer may send on, which is how many lane
+	// sessions we need in order to receive everything it sends.
+	PeerPortCount uint32
+	PeerBasePort  uint32
+	PeerTxLanes   uint32
 }
 
 // Machine drives a Noise handshake through N messages. It handles Noise
@@ -61,6 +69,7 @@ type Machine struct {
 	verifier       CertVerifier
 	result         *Result
 	msgs           []msgFlags
+	lanes          *LaneDetails // our multiport advert; nil emits a vanilla payload
 	myVersion      cert.Version
 	subtype        header.MessageSubType
 	indexAllocated bool
@@ -73,6 +82,8 @@ type Machine struct {
 // the noise pattern and the per-message content layout. The credential for
 // `version` is fetched via getCred and used to seed the noise.HandshakeState.
 // IndexAllocator is called lazily when the first outgoing payload is built.
+// lanes, when non-nil, is emitted as this side's multiport advert on every
+// payload-bearing message; nil produces byte-identical vanilla payloads.
 func NewMachine(
 	version cert.Version,
 	getCred GetCredentialFunc,
@@ -80,6 +91,7 @@ func NewMachine(
 	allocIndex IndexAllocator,
 	initiator bool,
 	subtype header.MessageSubType,
+	lanes *LaneDetails,
 ) (*Machine, error) {
 	info, err := subtypeInfoFor(subtype)
 	if err != nil {
@@ -103,6 +115,7 @@ func NewMachine(
 		getCred:    getCred,
 		allocIndex: allocIndex,
 		verifier:   verifier,
+		lanes:      lanes,
 		myVersion:  version,
 		result: &Result{
 			Initiator: initiator,
@@ -298,7 +311,8 @@ func (m *Machine) processPayload(msg []byte, flags msgFlags) error {
 	}
 
 	// Assert the payload contains exactly what we expect
-	hasPayloadData := payload.InitiatorIndex != 0 || payload.ResponderIndex != 0 || payload.Time != 0
+	hasPayloadData := payload.InitiatorIndex != 0 || payload.ResponderIndex != 0 || payload.Time != 0 ||
+		payload.InitiatorLanes != nil || payload.ResponderLanes != nil
 	if hasPayloadData != flags.expectsPayload {
 		m.failed = true
 		return ErrUnexpectedContent
@@ -327,6 +341,23 @@ func (m *Machine) processPayload(msg []byte, flags msgFlags) error {
 		m.result.RemoteIndex = remoteIndex
 		m.result.HandshakeTime = payload.Time
 		m.payloadSet = true
+
+		// Multiport advert from the peer's side of the exchange. Out-of-range
+		// values mean a peer we can't pair lanes with; ignore the advert
+		// rather than failing the handshake — the tunnel itself is fine, it
+		// just won't get lanes. Semantic policing (port-count caps, lane
+		// clamping) belongs to the handshake manager.
+		var peerLanes *LaneDetails
+		if m.result.Initiator {
+			peerLanes = payload.ResponderLanes
+		} else {
+			peerLanes = payload.InitiatorLanes
+		}
+		if peerLanes != nil && peerLanes.BasePort <= 0xffff && peerLanes.PortCount <= 0xffff && peerLanes.TxLanes <= 0xffff {
+			m.result.PeerPortCount = peerLanes.PortCount
+			m.result.PeerBasePort = peerLanes.BasePort
+			m.result.PeerTxLanes = peerLanes.TxLanes
+		}
 	}
 
 	// Process certificate
@@ -397,9 +428,11 @@ func (m *Machine) marshalOutgoing(flags msgFlags) ([]byte, error) {
 
 		if m.result.Initiator {
 			p.InitiatorIndex = m.result.LocalIndex
+			p.InitiatorLanes = m.lanes
 		} else {
 			p.ResponderIndex = m.result.LocalIndex
 			p.InitiatorIndex = m.result.RemoteIndex
+			p.ResponderLanes = m.lanes
 		}
 		p.Time = uint64(time.Now().UnixNano())
 	}

handshake/machine_lanes_test.go

@@ -0,0 +1,111 @@
+package handshake
+
+import (
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/slackhq/nebula/cert"
+	ct "github.com/slackhq/nebula/cert_test"
+	"github.com/slackhq/nebula/header"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// newTestLaneMachine is newTestMachine with a lane advert attached.
+func newTestLaneMachine(
+	t *testing.T,
+	cs *testCertState,
+	verifier CertVerifier,
+	initiator bool,
+	localIndex uint32,
+	lanes *LaneDetails,
+) *Machine {
+	t.Helper()
+	m, err := NewMachine(
+		cs.version, cs.getCredential,
+		verifier, func() (uint32, error) { return localIndex, nil },
+		initiator, header.HandshakeIXPSK0,
+		lanes,
+	)
+	require.NoError(t, err)
+	return m
+}
+
+func doFullLaneHandshake(t *testing.T, initLanes, respLanes *LaneDetails) (initR, respR *Result) {
+	t.Helper()
+	ca, _, caKey, _ := ct.NewTestCaCert(
+		cert.Version2, cert.Curve_CURVE25519, time.Time{}, time.Time{}, nil, nil, nil,
+	)
+	caPool := ct.NewTestCAPool(ca)
+	v := testVerifier(caPool)
+
+	initCS := newTestCertState(t, ca, caKey, "initiator", []netip.Prefix{netip.MustParsePrefix("10.0.0.1/24")})
+	respCS := newTestCertState(t, ca, caKey, "responder", []netip.Prefix{netip.MustParsePrefix("10.0.0.2/24")})
+
+	initM := newTestLaneMachine(t, initCS, v, true, 1000, initLanes)
+	respM := newTestLaneMachine(t, respCS, v, false, 2000, respLanes)
+
+	msg1, err := initM.Initiate(nil)
+	require.NoError(t, err)
+
+	resp, respR, err := respM.ProcessPacket(nil, msg1)
+	require.NoError(t, err)
+	require.NotNil(t, respR)
+
+	_, initR, err = initM.ProcessPacket(nil, resp)
+	require.NoError(t, err)
+	require.NotNil(t, initR)
+	return initR, respR
+}
+
+func TestMachineLaneAdvertBothSides(t *testing.T) {
+	initR, respR := doFullLaneHandshake(t,
+		&LaneDetails{PortCount: 8, BasePort: 4242, TxLanes: 8},
+		&LaneDetails{PortCount: 4, BasePort: 5353, TxLanes: 3},
+	)
+
+	// Each side's Result carries the peer's advert.
+	assert.Equal(t, uint32(4), initR.PeerPortCount)
+	assert.Equal(t, uint32(5353), initR.PeerBasePort)
+	assert.Equal(t, uint32(3), initR.PeerTxLanes)
+
+	assert.Equal(t, uint32(8), respR.PeerPortCount)
+	assert.Equal(t, uint32(4242), respR.PeerBasePort)
+	assert.Equal(t, uint32(8), respR.PeerTxLanes)
+}
+
+func TestMachineLaneAdvertAsymmetric(t *testing.T) {
+	// Vanilla initiator, multiport responder and vice versa: the nil side
+	// yields all-zero peer fields on the other end.
+	initR, respR := doFullLaneHandshake(t, nil, &LaneDetails{PortCount: 4, BasePort: 5353})
+	assert.Equal(t, uint32(4), initR.PeerPortCount)
+	assert.Equal(t, uint32(0), respR.PeerPortCount)
+	assert.Equal(t, uint32(0), respR.PeerBasePort)
+
+	initR, respR = doFullLaneHandshake(t, &LaneDetails{PortCount: 8, BasePort: 4242}, nil)
+	assert.Equal(t, uint32(0), initR.PeerPortCount)
+	assert.Equal(t, uint32(8), respR.PeerPortCount)
+}
+
+func TestMachineLaneAdvertOutOfRangeIgnored(t *testing.T) {
+	// A BasePort that can't be a real UDP port is ignored, not fatal.
+	initR, respR := doFullLaneHandshake(t,
+		&LaneDetails{PortCount: 8, BasePort: 70000, TxLanes: 8},
+		&LaneDetails{PortCount: 4, BasePort: 5353, TxLanes: 4},
+	)
+	assert.Equal(t, uint32(0), respR.PeerPortCount)
+	assert.Equal(t, uint32(0), respR.PeerBasePort)
+	assert.Equal(t, uint32(0), respR.PeerTxLanes)
+	// The sane side still negotiates.
+	assert.Equal(t, uint32(4), initR.PeerPortCount)
+
+	// An out-of-range TxLanes drops the whole advert the same way: a lane index
+	// that does not fit the header is as unusable as an impossible port.
+	initR, respR = doFullLaneHandshake(t,
+		&LaneDetails{PortCount: 8, BasePort: 4242, TxLanes: 0x10000},
+		&LaneDetails{PortCount: 4, BasePort: 5353, TxLanes: 4},
+	)
+	assert.Equal(t, uint32(0), respR.PeerPortCount)
+	assert.Equal(t, uint32(4), initR.PeerPortCount)
+}

handshake/machine_test.go

@@ -444,6 +444,7 @@ func TestMachineThreeMessagePattern(t *testing.T) {
 		initCS.getCredential, v,
 		func() (uint32, error) { return 1000, nil },
 		true, header.HandshakeXXPSK0,
+		nil,
 	)
 	require.NoError(t, err)
 
@@ -452,6 +453,7 @@ func TestMachineThreeMessagePattern(t *testing.T) {
 		respCS.getCredential, v,
 		func() (uint32, error) { return 2000, nil },
 		false, header.HandshakeXXPSK0,
+		nil,
 	)
 	require.NoError(t, err)
 

handshake/payload.go

@@ -20,15 +20,40 @@ type Payload struct {
 	ResponderIndex uint32
 	Time           uint64
 	CertVersion    uint32
+
+	// Multiport lane negotiation; nil when the sender has multiport disabled
+	// (which keeps the encoded payload byte-identical to a vanilla one).
+	InitiatorLanes *LaneDetails
+	ResponderLanes *LaneDetails
+}
+
+// LaneDetails advertises multiport lane capability: the contiguous UDP port
+// range the sender bound, and how many lanes it may send on. The receiver needs
+// PortCount/BasePort to aim its own lanes and TxLanes to know how many lane
+// sessions to derive for receiving.
+type LaneDetails struct {
+	PortCount uint32
+	BasePort  uint32
+	TxLanes   uint32
 }
 
 // Proto field numbers for NebulaHandshakeDetails
 const (
-	fieldCert           = 1 // bytes
-	fieldInitiatorIndex = 2 // uint32
-	fieldResponderIndex = 3 // uint32
-	fieldTime           = 5 // uint64
-	fieldCertVersion    = 8 // uint32
+	fieldCert           = 1  // bytes
+	fieldInitiatorIndex = 2  // uint32
+	fieldResponderIndex = 3  // uint32
+	fieldTime           = 5  // uint64
+	fieldCertVersion    = 8  // uint32
+	fieldInitiatorLanes = 9  // LaneDetails
+	fieldResponderLanes = 10 // LaneDetails
+)
+
+// Proto field numbers for LaneDetails.
+// Field 3 was a per-lane handshake index and is permanently reserved.
+const (
+	fieldLanePortCount = 1 // uint32
+	fieldLaneBasePort  = 2 // uint32
+	fieldLaneTxLanes   = 4 // uint32
 )
 
 // MarshalPayload encodes a handshake payload in protobuf wire format compatible
@@ -57,6 +82,16 @@ func MarshalPayload(out []byte, p Payload) []byte {
 		details = protowire.AppendTag(details, fieldCertVersion, protowire.VarintType)
 		details = protowire.AppendVarint(details, uint64(p.CertVersion))
 	}
+	// Emitted last to keep the encoding in ascending field-number order, which
+	// is what protoc-gen-go would produce for the same message.
+	if p.InitiatorLanes != nil {
+		details = protowire.AppendTag(details, fieldInitiatorLanes, protowire.BytesType)
+		details = protowire.AppendBytes(details, p.InitiatorLanes.marshal(nil))
+	}
+	if p.ResponderLanes != nil {
+		details = protowire.AppendTag(details, fieldResponderLanes, protowire.BytesType)
+		details = protowire.AppendBytes(details, p.ResponderLanes.marshal(nil))
+	}
 
 	out = protowire.AppendTag(out, 1, protowire.BytesType)
 	out = protowire.AppendBytes(out, details)
@@ -64,6 +99,20 @@ func MarshalPayload(out []byte, p Payload) []byte {
 	return out
 }
 
+// marshal appends the LaneDetails submessage fields to out. All fields are
+// emitted unconditionally: a LaneDetails is only present at all when multiport
+// is negotiating, and explicit zeros keep the parser's presence semantics
+// trivial.
+func (d *LaneDetails) marshal(out []byte) []byte {
+	out = protowire.AppendTag(out, fieldLanePortCount, protowire.VarintType)
+	out = protowire.AppendVarint(out, uint64(d.PortCount))
+	out = protowire.AppendTag(out, fieldLaneBasePort, protowire.VarintType)
+	out = protowire.AppendVarint(out, uint64(d.BasePort))
+	out = protowire.AppendTag(out, fieldLaneTxLanes, protowire.VarintType)
+	out = protowire.AppendVarint(out, uint64(d.TxLanes))
+	return out
+}
+
 // UnmarshalPayload decodes a protobuf-encoded NebulaHandshake message.
 func UnmarshalPayload(b []byte) (Payload, error) {
 	var p Payload
@@ -161,6 +210,72 @@ func unmarshalPayloadDetails(p *Payload, b []byte) error {
 			}
 			p.CertVersion = uint32(v)
 			b = b[n:]
+		case fieldInitiatorLanes:
+			if typ != protowire.BytesType {
+				return errInvalidHandshakeDetails
+			}
+			v, n := protowire.ConsumeBytes(b)
+			if n < 0 {
+				return errInvalidHandshakeDetails
+			}
+			p.InitiatorLanes = new(LaneDetails)
+			if err := unmarshalLaneDetails(p.InitiatorLanes, v); err != nil {
+				return err
+			}
+			b = b[n:]
+		case fieldResponderLanes:
+			if typ != protowire.BytesType {
+				return errInvalidHandshakeDetails
+			}
+			v, n := protowire.ConsumeBytes(b)
+			if n < 0 {
+				return errInvalidHandshakeDetails
+			}
+			p.ResponderLanes = new(LaneDetails)
+			if err := unmarshalLaneDetails(p.ResponderLanes, v); err != nil {
+				return err
+			}
+			b = b[n:]
+		default:
+			n := protowire.ConsumeFieldValue(num, typ, b)
+			if n < 0 {
+				return errInvalidHandshakeDetails
+			}
+			b = b[n:]
+		}
+	}
+	return nil
+}
+
+func unmarshalLaneDetails(d *LaneDetails, b []byte) error {
+	for len(b) > 0 {
+		num, typ, n := protowire.ConsumeTag(b)
+		if n < 0 {
+			return errInvalidHandshakeDetails
+		}
+		b = b[n:]
+
+		// Same contract as the details parser: known fields hard-fail on a
+		// wire-type mismatch, unknown fields are skipped, repeated singular
+		// fields follow proto3 last-wins.
+		switch num {
+		case fieldLanePortCount, fieldLaneBasePort, fieldLaneTxLanes:
+			if typ != protowire.VarintType {
+				return errInvalidHandshakeDetails
+			}
+			v, n := protowire.ConsumeVarint(b)
+			if n < 0 || v > math.MaxUint32 {
+				return errInvalidHandshakeDetails
+			}
+			switch num {
+			case fieldLanePortCount:
+				d.PortCount = uint32(v)
+			case fieldLaneBasePort:
+				d.BasePort = uint32(v)
+			case fieldLaneTxLanes:
+				d.TxLanes = uint32(v)
+			}
+			b = b[n:]
 		default:
 			n := protowire.ConsumeFieldValue(num, typ, b)
 			if n < 0 {

handshake/payload_test.go

@@ -117,23 +117,134 @@ func TestPayloadUnknownFields(t *testing.T) {
 		assert.Equal(t, uint32(88), got.ResponderIndex)
 	})
 
-	t.Run("reserved fields 6 and 7 are skipped", func(t *testing.T) {
-		// Fields 6 and 7 are reserved in the proto definition
+	t.Run("unknown field inside LaneDetails is skipped", func(t *testing.T) {
+		var lane []byte
+		lane = protowire.AppendTag(lane, fieldLanePortCount, protowire.VarintType)
+		lane = protowire.AppendVarint(lane, 4)
+		lane = protowire.AppendTag(lane, 50, protowire.VarintType) // unknown subfield
+		lane = protowire.AppendVarint(lane, 9999)
+		lane = protowire.AppendTag(lane, fieldLaneBasePort, protowire.VarintType)
+		lane = protowire.AppendVarint(lane, 4242)
+
 		var details []byte
 		details = protowire.AppendTag(details, fieldInitiatorIndex, protowire.VarintType)
 		details = protowire.AppendVarint(details, 100)
-		details = protowire.AppendTag(details, 6, protowire.VarintType)
-		details = protowire.AppendVarint(details, 1)
-		details = protowire.AppendTag(details, 7, protowire.VarintType)
-		details = protowire.AppendVarint(details, 2)
+		details = protowire.AppendTag(details, fieldInitiatorLanes, protowire.BytesType)
+		details = protowire.AppendBytes(details, lane)
 
-		var data []byte
-		data = protowire.AppendTag(data, 1, protowire.BytesType)
-		data = protowire.AppendBytes(data, details)
+		got, err := UnmarshalPayload(wrapDetails(details))
+		require.NoError(t, err)
+		assert.Equal(t, uint32(100), got.InitiatorIndex)
+		require.NotNil(t, got.InitiatorLanes)
+		assert.Equal(t, uint32(4), got.InitiatorLanes.PortCount)
+		assert.Equal(t, uint32(4242), got.InitiatorLanes.BasePort)
+	})
+}
+
+func TestPayloadLaneDetails(t *testing.T) {
+	t.Run("round trip both sides", func(t *testing.T) {
+		data := MarshalPayload(nil, Payload{
+			InitiatorIndex: 12345,
+			Time:           999,
+			InitiatorLanes: &LaneDetails{PortCount: 8, BasePort: 4242, TxLanes: 3},
+			ResponderLanes: &LaneDetails{PortCount: 4, BasePort: 5353},
+		})
 
 		got, err := UnmarshalPayload(data)
 		require.NoError(t, err)
-		assert.Equal(t, uint32(100), got.InitiatorIndex)
+		require.NotNil(t, got.InitiatorLanes)
+		assert.Equal(t, LaneDetails{PortCount: 8, BasePort: 4242, TxLanes: 3}, *got.InitiatorLanes)
+		require.NotNil(t, got.ResponderLanes)
+		assert.Equal(t, LaneDetails{PortCount: 4, BasePort: 5353}, *got.ResponderLanes)
+	})
+
+	t.Run("zero-valued LaneDetails survives the round trip", func(t *testing.T) {
+		// Presence is what negotiation keys on; an all-zero advert must not
+		// decay to nil.
+		data := MarshalPayload(nil, Payload{
+			InitiatorIndex: 1,
+			InitiatorLanes: &LaneDetails{},
+		})
+		got, err := UnmarshalPayload(data)
+		require.NoError(t, err)
+		require.NotNil(t, got.InitiatorLanes)
+		assert.Equal(t, LaneDetails{}, *got.InitiatorLanes)
+		assert.Nil(t, got.ResponderLanes)
+	})
+
+	t.Run("nil lanes marshal byte-identical to a vanilla payload", func(t *testing.T) {
+		p := Payload{
+			Cert:           []byte("cert"),
+			CertVersion:    2,
+			InitiatorIndex: 100,
+			Time:           999,
+		}
+		// The vanilla encoding of the same fields, built by hand in field order.
+		var details []byte
+		details = protowire.AppendTag(details, fieldCert, protowire.BytesType)
+		details = protowire.AppendBytes(details, p.Cert)
+		details = protowire.AppendTag(details, fieldInitiatorIndex, protowire.VarintType)
+		details = protowire.AppendVarint(details, uint64(p.InitiatorIndex))
+		details = protowire.AppendTag(details, fieldTime, protowire.VarintType)
+		details = protowire.AppendVarint(details, p.Time)
+		details = protowire.AppendTag(details, fieldCertVersion, protowire.VarintType)
+		details = protowire.AppendVarint(details, uint64(p.CertVersion))
+
+		assert.Equal(t, wrapDetails(details), MarshalPayload(nil, p))
+	})
+
+	t.Run("lane field with wrong wire type rejected", func(t *testing.T) {
+		for _, field := range []protowire.Number{fieldInitiatorLanes, fieldResponderLanes} {
+			var details []byte
+			details = protowire.AppendTag(details, field, protowire.VarintType)
+			details = protowire.AppendVarint(details, 1)
+			_, err := UnmarshalPayload(wrapDetails(details))
+			assert.Error(t, err)
+		}
+	})
+
+	t.Run("lane subfield with wrong wire type rejected", func(t *testing.T) {
+		var lane []byte
+		lane = protowire.AppendTag(lane, fieldLanePortCount, protowire.BytesType)
+		lane = protowire.AppendBytes(lane, []byte{1, 2, 3})
+
+		var details []byte
+		details = protowire.AppendTag(details, fieldInitiatorLanes, protowire.BytesType)
+		details = protowire.AppendBytes(details, lane)
+		_, err := UnmarshalPayload(wrapDetails(details))
+		assert.Error(t, err)
+	})
+
+	t.Run("truncated LaneDetails submessage rejected", func(t *testing.T) {
+		var details []byte
+		details = protowire.AppendTag(details, fieldInitiatorLanes, protowire.BytesType)
+		details = append(details, 0x0a, 0x01, 0x02) // length 10, only 2 bytes
+		_, err := UnmarshalPayload(wrapDetails(details))
+		assert.Error(t, err)
+	})
+
+	t.Run("truncated varint inside LaneDetails rejected", func(t *testing.T) {
+		var lane []byte
+		lane = protowire.AppendTag(lane, fieldLaneBasePort, protowire.VarintType)
+		lane = append(lane, 0x80) // incomplete varint
+
+		var details []byte
+		details = protowire.AppendTag(details, fieldResponderLanes, protowire.BytesType)
+		details = protowire.AppendBytes(details, lane)
+		_, err := UnmarshalPayload(wrapDetails(details))
+		assert.Error(t, err)
+	})
+
+	t.Run("lane subfield varint overflow rejected", func(t *testing.T) {
+		var lane []byte
+		lane = protowire.AppendTag(lane, fieldLaneTxLanes, protowire.VarintType)
+		lane = protowire.AppendVarint(lane, math.MaxUint32+1)
+
+		var details []byte
+		details = protowire.AppendTag(details, fieldInitiatorLanes, protowire.BytesType)
+		details = protowire.AppendBytes(details, lane)
+		_, err := UnmarshalPayload(wrapDetails(details))
+		assert.Error(t, err)
 	})
 }
 
@@ -328,6 +439,12 @@ func FuzzPayload(f *testing.F) {
 		Time:           3,
 		CertVersion:    2,
 	}))
+	f.Add(MarshalPayload(nil, Payload{
+		InitiatorIndex: 1,
+		Time:           3,
+		InitiatorLanes: &LaneDetails{PortCount: 8, BasePort: 4242, TxLanes: 2},
+		ResponderLanes: &LaneDetails{PortCount: 4, BasePort: 5353},
+	}))
 	f.Add([]byte{})
 	f.Add([]byte{0xff})
 
@@ -357,5 +474,14 @@ func payloadsEqual(a, b Payload) bool {
 		a.InitiatorIndex == b.InitiatorIndex &&
 		a.ResponderIndex == b.ResponderIndex &&
 		a.Time == b.Time &&
-		a.CertVersion == b.CertVersion
+		a.CertVersion == b.CertVersion &&
+		laneDetailsEqual(a.InitiatorLanes, b.InitiatorLanes) &&
+		laneDetailsEqual(a.ResponderLanes, b.ResponderLanes)
+}
+
+func laneDetailsEqual(a, b *LaneDetails) bool {
+	if a == nil || b == nil {
+		return a == b
+	}
+	return *a == *b
 }

handshake_manager.go

@@ -50,6 +50,14 @@ type HandshakeConfig struct {
 	retries       int64
 	triggerBuffer int
 
+	// Multiport lane parameters; laneCount == 0 means multiport is disabled.
+	// laneCount includes implicit lane 0 (the base tunnel), so lanes
+	// 1..laneCount-1 may carry traffic. lanePortCount/laneBasePort describe our
+	// own bound port range and are advertised in every handshake payload.
+	laneCount     int
+	lanePortCount uint16
+	laneBasePort  uint16
+
 	messageMetrics *MessageMetrics
 }
 
@@ -295,7 +303,13 @@ func (hm *HandshakeManager) handleOutbound(vpnIp netip.Addr, lighthouseTriggered
 		hm.messageMetrics.Tx(header.Handshake, hh.machine.Subtype(), 1)
 		err := hm.outside.WriteTo(stage0, addr)
 		if err != nil {
-			hostinfo.logger(hm.l).Error("Failed to send handshake message",
+			// These repeat every attempt, so match the success log below and only shout when the remotes changed
+			level := slog.LevelDebug
+			if remotesHaveChanged {
+				level = slog.LevelError
+			}
+
+			hostinfo.logger(hm.l).Log(context.Background(), level, "Failed to send handshake message",
 				"udpAddr", addr,
 				"initiatorIndex", hostinfo.localIndexId,
 				"handshake", hsFields,
@@ -430,14 +444,11 @@ func (hm *HandshakeManager) CheckAndComplete(hostinfo *HostInfo, handshakePacket
 	// Check if we already have a tunnel with this vpn ip
 	existingHostInfo, found := hm.mainHostMap.Hosts[hostinfo.vpnAddrs[0]]
 	if found && existingHostInfo != nil {
-		testHostInfo := existingHostInfo
-		for testHostInfo != nil {
-			// Is it just a delayed handshake packet?
+		// Is it just a delayed handshake packet? Check every hostinfo we hold for this address.
+		for _, testHostInfo := range hm.mainHostMap.unlockedGetHostList(hostinfo.vpnAddrs[0]) {
 			if bytes.Equal(hostinfo.HandshakePacket[handshakePacket], testHostInfo.HandshakePacket[handshakePacket]) {
 				return testHostInfo, ErrAlreadySeen
 			}
-
-			testHostInfo = testHostInfo.next
 		}
 
 		// Is this a newer handshake?
@@ -532,7 +543,12 @@ func (hm *HandshakeManager) DeleteHostInfo(hostinfo *HostInfo) {
 
 func (hm *HandshakeManager) unlockedDeleteHostInfo(hostinfo *HostInfo) {
 	for _, addr := range hostinfo.vpnAddrs {
-		delete(hm.vpnIps, addr)
+		// Only delete the pending entry if it is actually ours: an
+		// unconditional delete could evict a concurrently pending handshake for
+		// the same address.
+		if cur, ok := hm.vpnIps[addr]; ok && cur.hostinfo == hostinfo {
+			delete(hm.vpnIps, addr)
+		}
 	}
 
 	if len(hm.vpnIps) == 0 {
@@ -667,6 +683,7 @@ func (hm *HandshakeManager) buildStage0Packet(hh *HandshakeHostInfo) bool {
 		v, cs.GetCredential,
 		hm.certVerifier(), func() (uint32, error) { return hm.allocateIndex(hh) },
 		true, header.HandshakeIXPSK0,
+		hm.laneAdvert(),
 	)
 	if err != nil {
 		hm.f.l.Error("Failed to create handshake machine",
@@ -690,6 +707,35 @@ func (hm *HandshakeManager) buildStage0Packet(hh *HandshakeHostInfo) bool {
 	return true
 }
 
+// laneAdvert returns our multiport advert for a handshake payload, or nil
+// when multiport is disabled (which keeps the payload byte-identical to
+// vanilla).
+func (hm *HandshakeManager) laneAdvert() *handshake.LaneDetails {
+	if hm.config.laneCount == 0 {
+		return nil
+	}
+	return &handshake.LaneDetails{
+		PortCount: uint32(hm.config.lanePortCount),
+		BasePort:  uint32(hm.config.laneBasePort),
+		TxLanes:   uint32(hm.config.laneCount),
+	}
+}
+
+// maybeAllocLanes sets up the multiport lanes for a just-completed tunnel. Must
+// run before the hostinfo becomes visible in the hostmap: the data plane reads
+// hostinfo.lanes without synchronizing on it. The sessions themselves are derived
+// later, on the first packet that needs each one.
+func (hm *HandshakeManager) maybeAllocLanes(hostinfo *HostInfo, result *handshake.Result) {
+	if hm.config.laneCount == 0 || result.PeerPortCount == 0 {
+		return
+	}
+	if len(hm.f.myVpnAddrs) == 0 || len(hostinfo.vpnAddrs) == 0 {
+		return
+	}
+
+	hostinfo.lanes = newLaneSet(result, hm.config.laneCount, hm.f.myVpnAddrs[0], hostinfo.vpnAddrs[0])
+}
+
 // beginHandshake handles an incoming handshake packet that doesn't match any
 // existing pending handshake. It creates a new responder Machine and processes
 // the first message.
@@ -708,6 +754,7 @@ func (hm *HandshakeManager) beginHandshake(via ViaSender, packet []byte, h *head
 		v, cs.GetCredential,
 		hm.certVerifier(), func() (uint32, error) { return generateIndex(f.l) },
 		false, header.HandshakeIXPSK0,
+		hm.laneAdvert(),
 	)
 	if err != nil {
 		f.l.Error("Failed to create handshake machine", "from", via, "error", err)
@@ -744,8 +791,14 @@ func (hm *HandshakeManager) beginHandshake(via ViaSender, packet []byte, h *head
 		return
 	}
 
+	connState, err := newConnectionStateFromResult(result)
+	if err != nil {
+		f.l.Error("Discarding handshake with an invalid message index", "error", err, "vpnAddrs", vpnAddrs)
+		return
+	}
+
 	hostinfo := &HostInfo{
-		ConnectionState:   newConnectionStateFromResult(result),
+		ConnectionState:   connState,
 		localIndexId:      result.LocalIndex,
 		remoteIndexId:     result.RemoteIndex,
 		vpnAddrs:          vpnAddrs,
@@ -758,6 +811,10 @@ func (hm *HandshakeManager) beginHandshake(via ViaSender, packet []byte, h *head
 		},
 	}
 
+	// Lanes are allocated before the log line so it can report what was actually
+	// negotiated, and must in any case be in place before CheckAndComplete below.
+	hm.maybeAllocLanes(hostinfo, result)
+
 	msg := "Handshake message received"
 	if !anyVpnAddrsInCommon {
 		msg = "Handshake message received, but no vpnNetworks in common."
@@ -772,6 +829,7 @@ func (hm *HandshakeManager) beginHandshake(via ViaSender, packet []byte, h *head
 		"initiatorIndex", result.RemoteIndex,
 		"responderIndex", result.LocalIndex,
 		"handshake", m{"stage": uint64(machine.MessageIndex()), "style": header.SubTypeName(header.Handshake, machine.Subtype())},
+		laneLogAttr(hm.config.laneCount, hostinfo.lanes),
 	)
 
 	// packet aliases the listener's incoming buffer, so this copy must stay.
@@ -863,7 +921,13 @@ func (hm *HandshakeManager) continueHandshake(via ViaSender, hh *HandshakeHostIn
 	}
 
 	// Handshake complete; build the ConnectionState now that we have keys and a verified peer cert.
-	hostinfo.ConnectionState = newConnectionStateFromResult(result)
+	cs, err := newConnectionStateFromResult(result)
+	if err != nil {
+		f.l.Error("Discarding handshake with an invalid message index", "error", err, "vpnAddrs", hostinfo.vpnAddrs)
+		hm.DeleteHostInfo(hostinfo)
+		return
+	}
+	hostinfo.ConnectionState = cs
 
 	remoteCert := result.RemoteCert
 	if remoteCert == nil {
@@ -940,6 +1004,14 @@ func (hm *HandshakeManager) continueHandshake(via ViaSender, hh *HandshakeHostIn
 	}
 
 	duration := time.Since(hh.startTime).Nanoseconds()
+
+	hostinfo.vpnAddrs = vpnAddrs
+	hostinfo.buildNetworks(f.myVpnNetworksTable, remoteCert.Certificate)
+
+	// Lanes are allocated before the log line so it can report what was actually
+	// negotiated, and must in any case be in place before Complete below.
+	hm.maybeAllocLanes(hostinfo, result)
+
 	msg := "Handshake message received"
 	if !anyVpnAddrsInCommon {
 		msg = "Handshake message received, but no vpnNetworks in common."
@@ -956,11 +1028,9 @@ func (hm *HandshakeManager) continueHandshake(via ViaSender, hh *HandshakeHostIn
 		"handshake", m{"stage": uint64(machine.MessageIndex()), "style": header.SubTypeName(header.Handshake, machine.Subtype())},
 		"durationNs", duration,
 		"sentCachedPackets", len(hh.packetStore),
+		laneLogAttr(hm.config.laneCount, hostinfo.lanes),
 	)
 
-	hostinfo.vpnAddrs = vpnAddrs
-	hostinfo.buildNetworks(f.myVpnNetworksTable, remoteCert.Certificate)
-
 	hm.Complete(hostinfo, f)
 
 	if len(hh.packetStore) > 0 {
@@ -970,6 +1040,9 @@ func (hm *HandshakeManager) continueHandshake(via ViaSender, hh *HandshakeHostIn
 		nb := make([]byte, 12, 12)
 		out := make([]byte, mtu)
 		for _, cp := range hh.packetStore {
+			// TODO: use a SendBatch here. Each callback lands in
+			// sendNoMetrics -> WriteTo: one syscall per cached packet,
+			// where one sendmmsg could flush the whole store.
 			cp.callback(cp.messageType, cp.messageSubType, hostinfo, cp.packet, nb, out)
 		}
 		f.cachedPacketMetrics.sent.Inc(int64(len(hh.packetStore)))
@@ -1066,7 +1139,10 @@ func (hm *HandshakeManager) sendHandshakeResponse(via ViaSender, msg []byte, hos
 
 	if !via.IsRelayed {
 		fields := append(logFields, "from", via)
-		err := f.outside.WriteTo(msg, via.UdpAddr)
+		// Reply from the socket the handshake arrived on so the initiator sees
+		// the source port it targeted. Identical to f.outside under vanilla
+		// config (all writers share one port); required for multiport lanes.
+		err := f.writers[via.SockIdx].WriteTo(msg, via.UdpAddr)
 		if err != nil {
 			f.l.Error("Failed to send handshake message", append(fields, "error", err)...)
 		} else {
@@ -1080,8 +1156,8 @@ func (hm *HandshakeManager) sendHandshakeResponse(via ViaSender, msg []byte, hos
 		hostinfo.relayState.InsertRelayTo(via.relayHI.vpnAddrs[0])
 		// We received a valid handshake on this relay, so make sure the relay
 		// state reflects that, in case it had been marked Disestablished.
-		via.relayHI.relayState.UpdateRelayForByIdxState(via.remoteIdx, Established)
-		f.SendVia(via.relayHI, via.relay, msg, make([]byte, 12), make([]byte, mtu), false)
+		via.relayHI.relayState.UpdateRelayForByIdxState(via.relay.LocalIndex, Established)
+		f.SendVia(via.relayHI, via.relay, msg, make([]byte, 12), make([]byte, mtu), false, 0)
 		f.l.Info("Handshake message sent", append(logFields, "relay", via.relayHI.vpnAddrs[0])...)
 	}
 }

handshake_manager_test.go

@@ -84,7 +84,7 @@ func (mw *mockEncWriter) SendMessageToVpnAddr(_ header.MessageType, _ header.Mes
 	return
 }
 
-func (mw *mockEncWriter) SendVia(_ *HostInfo, _ *Relay, _, _, _ []byte, _ bool) {
+func (mw *mockEncWriter) SendVia(via *HostInfo, relay *Relay, ad, nb, out []byte, nocopy bool, q int) {
 	return
 }
 

header/header.go

@@ -8,16 +8,28 @@ import (
 )
 
 //Version 1 header:
-// 0                                                                       31
-// |-----------------------------------------------------------------------|
-// | Version (uint4) | Type (uint4) |  Subtype (uint8) | Reserved (uint16) | 32
-// |-----------------------------------------------------------------------|
-// |                        Remote index (uint32)                          | 64
-// |-----------------------------------------------------------------------|
-// |                           Message counter                             | 96
-// |                               (uint64)                                | 128
-// |-----------------------------------------------------------------------|
-// |                               payload...                              |
+// 0                                                                                  31
+// |------------------------------------------------------------------------------------|
+// | Version (uint4) | Type (uint4) | Subtype (uint8) | Reserved (uint8) | Lane (uint8) | 32
+// |------------------------------------------------------------------------------------|
+// |                               Remote index (uint32)                                | 64
+// |------------------------------------------------------------------------------------|
+// |                                  Message counter                                   | 96
+// |                                      (uint64)                                      | 128
+// |------------------------------------------------------------------------------------|
+// |                                     payload...                                     |
+//
+// Lane is the multiport lane index, carved out of the low 8 bits of what was a
+// single Reserved (uint16) before multiport. Lane 0 is the base tunnel, which is
+// what every sender that does not know about lanes emits and what every non-lane
+// packet — handshakes, lighthouse, relays, close — carries, so the field is
+// compatible in both directions with a peer that has never heard of it. The
+// remaining 8 bits stay reserved and are always sent as zero. The H struct still
+// holds the pair as one Reserved field; use H.Lane and EncodeLane to reach the
+// low byte.
+//
+// Lane is part of the AEAD's associated data, so a lane index cannot be altered
+// in flight: a packet decrypts on the lane it claims or not at all.
 
 type m = map[string]any
 
@@ -57,8 +69,18 @@ const (
 const (
 	TestRequest MessageSubType = 0
 	TestReply   MessageSubType = 1
+	// LaneProbe is sent on a multiport lane to prove the lane's 5-tuple is
+	// usable; LaneProbeAck answers it on the base tunnel.
+	LaneProbe    MessageSubType = 2
+	LaneProbeAck MessageSubType = 3
 )
 
+// MaxLane is the largest lane index the header can carry.
+const MaxLane = 0xff
+
+// laneMask covers the bits of Reserved that hold the lane index.
+const laneMask uint16 = 0x00ff
+
 const (
 	HandshakeIXPSK0 MessageSubType = 0
 	HandshakeXXPSK0 MessageSubType = 1
@@ -67,8 +89,10 @@ const (
 var ErrHeaderTooShort = errors.New("header is too short")
 
 var subTypeTestMap = map[MessageSubType]string{
-	TestRequest: "testRequest",
-	TestReply:   "testReply",
+	TestRequest:  "testRequest",
+	TestReply:    "testReply",
+	LaneProbe:    "laneProbe",
+	LaneProbeAck: "laneProbeAck",
 }
 
 var subTypeNoneMap = map[MessageSubType]string{0: "none"}
@@ -100,10 +124,16 @@ type H struct {
 // Encode uses the provided byte array to encode the provided header values into.
 // Byte array must be capped higher than HeaderLen or this will panic
 func Encode(b []byte, v uint8, t MessageType, st MessageSubType, ri uint32, c uint64) []byte {
+	return EncodeLane(b, v, t, st, ri, c, 0)
+}
+
+// EncodeLane is Encode with an explicit multiport lane index, which is carried
+// in the low 8 bits of Reserved.
+func EncodeLane(b []byte, v uint8, t MessageType, st MessageSubType, ri uint32, c uint64, lane uint8) []byte {
 	b = b[:Len]
 	b[0] = v<<4 | byte(t&0x0f)
 	b[1] = byte(st)
-	binary.BigEndian.PutUint16(b[2:4], 0)
+	binary.BigEndian.PutUint16(b[2:4], uint16(lane))
 	binary.BigEndian.PutUint32(b[4:8], ri)
 	binary.BigEndian.PutUint64(b[8:16], c)
 	return b
@@ -136,7 +166,13 @@ func (h *H) Encode(b []byte) ([]byte, error) {
 		return nil, errors.New("nil header")
 	}
 
-	return Encode(b, h.Version, h.Type, h.Subtype, h.RemoteIndex, h.MessageCounter), nil
+	return EncodeLane(b, h.Version, h.Type, h.Subtype, h.RemoteIndex, h.MessageCounter, h.Lane()), nil
+}
+
+// Lane returns the multiport lane index carried in Reserved. Lane 0 is the base
+// tunnel, which is what any sender that does not know about lanes will report.
+func (h *H) Lane() uint8 {
+	return uint8(h.Reserved & laneMask)
 }
 
 // Parse is a helper function to parses given bytes into new Header struct
@@ -190,13 +226,18 @@ func SubTypeName(t MessageType, s MessageSubType) string {
 }
 
 func IsValidSubType(t MessageType, s MessageSubType) bool {
-	if n, ok := subTypeMap[t]; ok {
-		if _, ok := (*n)[s]; ok {
-			return true
-		}
+	switch t {
+	case Message:
+		return s == MessageNone || s == MessageRelay
+	case Handshake:
+		return s == HandshakeIXPSK0
+	case Test:
+		return s == TestReply || s == TestRequest || s == LaneProbe || s == LaneProbeAck
+	case Control, CloseTunnel, RecvError, LightHouse:
+		return s == 0
+	default:
+		return false
 	}
-
-	return false
 }
 
 // NewHeader turns bytes into a header

header/header_test.go

@@ -52,6 +52,28 @@ func TestParse(t *testing.T) {
 	}
 }
 
+func TestEncodeLane(t *testing.T) {
+	b := EncodeLane(make([]byte, Len), Version, Message, MessageNone, 10, 9, 3)
+	assert.Equal(t, []byte{0x11, 0x0, 0x0, 0x3}, b[:4])
+
+	h := &H{}
+	require.NoError(t, h.Parse(b))
+	assert.Equal(t, uint16(3), h.Reserved)
+	assert.Equal(t, uint8(3), h.Lane())
+
+	// Encode is EncodeLane on the base tunnel, and the H method round trips the lane.
+	assert.Equal(t,
+		EncodeLane(make([]byte, Len), Version, Message, MessageNone, 10, 9, 0),
+		Encode(make([]byte, Len), Version, Message, MessageNone, 10, 9))
+
+	rt, err := h.Encode(make([]byte, Len))
+	require.NoError(t, err)
+	assert.Equal(t, b, rt)
+
+	// Only the low 8 bits of Reserved are the lane.
+	assert.Equal(t, uint8(0x2a), (&H{Reserved: 0xff2a}).Lane())
+}
+
 func TestTypeName(t *testing.T) {
 	assert.Equal(t, "test", TypeName(Test))
 	assert.Equal(t, "test", (&H{Type: Test}).TypeName())
@@ -102,6 +124,59 @@ func TestTypeMap(t *testing.T) {
 	}, subTypeMap)
 }
 
+// mapIsValidSubType is the pre-refactor, map-driven definition of a valid
+// subtype. IsValidSubType was reimplemented as an explicit switch; this keeps
+// the original behavior around so we can prove the switch is equivalent to it.
+func mapIsValidSubType(t MessageType, s MessageSubType) bool {
+	if n, ok := subTypeMap[t]; ok {
+		if _, ok := (*n)[s]; ok {
+			return true
+		}
+	}
+	return false
+}
+
+func TestIsValidSubType(t *testing.T) {
+	// Explicit intent table: documents exactly which subtypes are valid so the
+	// test stays meaningful even if both the switch and subTypeMap change.
+	assert.True(t, IsValidSubType(Message, MessageNone))
+	assert.True(t, IsValidSubType(Message, MessageRelay))
+	assert.False(t, IsValidSubType(Message, 2))
+
+	assert.True(t, IsValidSubType(Handshake, HandshakeIXPSK0))
+	// HandshakeXXPSK0 is defined but not a wire-valid subtype.
+	assert.False(t, IsValidSubType(Handshake, HandshakeXXPSK0))
+
+	assert.True(t, IsValidSubType(Test, TestRequest))
+	assert.True(t, IsValidSubType(Test, TestReply))
+	assert.True(t, IsValidSubType(Test, LaneProbe))
+	assert.True(t, IsValidSubType(Test, LaneProbeAck))
+	assert.False(t, IsValidSubType(Test, 4))
+
+	// These types only ever carry subtype 0.
+	for _, mt := range []MessageType{Control, CloseTunnel, RecvError, LightHouse} {
+		assert.True(t, IsValidSubType(mt, 0), "type %d subtype 0 should be valid", mt)
+		assert.False(t, IsValidSubType(mt, 1), "type %d subtype 1 should be invalid", mt)
+	}
+
+	// Unknown/unassigned types are never valid.
+	assert.False(t, IsValidSubType(99, 0))
+
+	// Exhaustive proof of equivalence with the original map-driven logic across
+	// the entire (type, subtype) input space.
+	for ti := 0; ti <= 0xff; ti++ {
+		for si := 0; si <= 0xff; si++ {
+			mt, mst := MessageType(ti), MessageSubType(si)
+			assert.Equalf(t, mapIsValidSubType(mt, mst), IsValidSubType(mt, mst),
+				"IsValidSubType(%d, %d) diverged from map-driven definition", ti, si)
+		}
+	}
+
+	// H method must delegate to the package function.
+	assert.True(t, (&H{Type: Test, Subtype: TestReply}).IsValidSubType())
+	assert.False(t, (&H{Type: Handshake, Subtype: HandshakeXXPSK0}).IsValidSubType())
+}
+
 func TestHeader_String(t *testing.T) {
 	assert.Equal(
 		t,

hostmap.go

@@ -56,11 +56,20 @@ type Relay struct {
 }
 
 type HostMap struct {
-	sync.RWMutex    //Because we concurrently read and write to our maps
-	Indexes         map[uint32]*HostInfo
-	Relays          map[uint32]*HostInfo // Maps a Relay IDX to a Relay HostInfo object
-	RemoteIndexes   map[uint32]*HostInfo
+	sync.RWMutex  //Because we concurrently read and write to our maps
+	Indexes       map[uint32]*HostInfo
+	Relays        map[uint32]*HostInfo // Maps a Relay IDX to a Relay HostInfo object
+	RemoteIndexes map[uint32]*HostInfo
+	// Hosts maps a vpn address to its primary hostinfo, one entry per address we hold a tunnel
+	// for. moreHosts only has an entry while an address is held by 2 or more hostinfos and stores
+	// the full most-recent-first list; moreHosts[a][0] is always the same hostinfo as Hosts[a].
+	// Each address gets its own independent list, so a hostinfo owning multiple addresses can
+	// never corrupt another address's ordering the way the old shared next/prev chain could.
+	// Entries in moreHosts are only ever written by unlockedSetHostsForAddr; Hosts is written
+	// directly only in the single-hostinfo fast paths where moreHosts is known to have no entry,
+	// and unlockedDeleteHostInfo swaps either map for a fresh one when it fully drains.
 	Hosts           map[netip.Addr]*HostInfo
+	moreHosts       map[netip.Addr][]*HostInfo
 	preferredRanges atomic.Pointer[[]netip.Prefix]
 	l               *slog.Logger
 }
@@ -230,11 +239,15 @@ const (
 
 type HostInfo struct {
 	remote          atomic.Pointer[netip.AddrPort]
-	remotes         *RemoteList
-	promoteCounter  atomic.Uint32
 	ConnectionState *ConnectionState
-	remoteIndexId   uint32
-	localIndexId    uint32
+
+	// Traffic bits, pendingDeletion, and the rebind epoch we last sent under
+	state atomic.Uint32
+
+	promoteCounter atomic.Uint32
+	remoteIndexId  uint32
+	localIndexId   uint32
+	remotes        *RemoteList
 
 	// vpnAddrs is a list of vpn addresses assigned to this host that are within our own vpn networks
 	// The host may have other vpn addresses that are outside our
@@ -253,11 +266,6 @@ type HostInfo struct {
 	// This is used to limit lighthouse re-queries in chatty clients
 	nextLHQuery atomic.Int64
 
-	// lastRebindCount is the other side of Interface.rebindCount, if these values don't match then we need to ask LH
-	// for a punch from the remote end of this tunnel. The goal being to prime their conntrack for our traffic just like
-	// with a handshake
-	lastRebindCount int8
-
 	// lastHandshakeTime records the time the remote side told us about at the stage when the handshake was completed locally
 	// Stage 1 packet will contain it if I am a responder, stage 2 packet if I am an initiator
 	// This is used to avoid an attack where a handshake packet is replayed after some time
@@ -266,25 +274,27 @@ type HostInfo struct {
 	lastRoam       time.Time
 	lastRoamRemote netip.AddrPort
 
-	// Used to track other hostinfos for this vpn ip since only 1 can be primary
-	// Synchronised via hostmap lock and not the hostinfo lock.
-	next, prev *HostInfo
-
-	//TODO: in, out, and others might benefit from being an atomic.Int32. We could collapse connectionManager pendingDeletion, relayUsed, and in/out into this 1 thing
-	in, out, pendingDeletion atomic.Bool
-
 	// lastUsed tracks the last time ConnectionManager checked the tunnel and it was in use.
 	// This value will be behind against actual tunnel utilization in the hot path.
 	// This should only be used by the ConnectionManagers ticker routine.
 	lastUsed time.Time
+
+	// lanes holds this tunnel's multiport lane sessions. Allocated when the
+	// handshake completes if both sides advertised multiport, nil otherwise.
+	// Immutable once the hostinfo is published to the data plane.
+	lanes *laneSet
 }
 
 type ViaSender struct {
 	UdpAddr   netip.AddrPort
 	relayHI   *HostInfo // relayHI is the host info object of the relay
-	remoteIdx uint32    // remoteIdx is the index included in the header of the received packet
 	relay     *Relay    // relay contains the rest of the relay information, including the PeerIP of the host trying to communicate with us.
 	IsRelayed bool      // IsRelayed is true if the packet was sent through a relay
+
+	// SockIdx is the local socket (Interface.writers index) the packet
+	// arrived on. Replies that must originate from the same 4-tuple egress
+	// f.writers[SockIdx].
+	SockIdx int
 }
 
 func (v ViaSender) String() string {
@@ -334,6 +344,7 @@ func newHostMap(l *slog.Logger) *HostMap {
 		Relays:        map[uint32]*HostInfo{},
 		RemoteIndexes: map[uint32]*HostInfo{},
 		Hosts:         map[netip.Addr]*HostInfo{},
+		moreHosts:     map[netip.Addr][]*HostInfo{},
 		l:             l,
 	}
 }
@@ -382,13 +393,55 @@ func (hm *HostMap) EmitStats() {
 	metrics.GetOrRegisterGauge("hostmap.main.relayIndexes", nil).Update(int64(relaysLen))
 }
 
-// DeleteHostInfo will fully unlink the hostinfo and return true if it was the final hostinfo for this vpn ip
+// unlockedSetHostsForAddr stores the per-address hostinfo list (list[0] is the primary). An empty
+// list removes the address. This is the one place Hosts and moreHosts are written together, keep
+// it that way. Callers must hold the write lock.
+func (hm *HostMap) unlockedSetHostsForAddr(addr netip.Addr, list []*HostInfo) {
+	if len(list) == 0 {
+		delete(hm.Hosts, addr)
+		delete(hm.moreHosts, addr)
+		return
+	}
+	hm.Hosts[addr] = list[0]
+	if len(list) > 1 {
+		hm.moreHosts[addr] = list
+	} else {
+		delete(hm.moreHosts, addr)
+	}
+}
+
+// unlockedGetHostList returns every hostinfo holding addr, primary first, or nil if we have no
+// tunnel for addr. The common single-hostinfo case builds a fresh one element list, so keep this
+// off the packet hot path; the primary is a direct Hosts read. Callers must hold the lock (read
+// or write).
+func (hm *HostMap) unlockedGetHostList(addr netip.Addr) []*HostInfo {
+	if list, ok := hm.moreHosts[addr]; ok {
+		return list
+	}
+	if h, ok := hm.Hosts[addr]; ok {
+		return []*HostInfo{h}
+	}
+	return nil
+}
+
+// removeHostInfo returns list with hi removed (order preserved), or list unchanged if hi is
+// absent. It deletes in place: every mutator holds the hostmap write lock and no reader ever
+// retains a slice across a mutation (readers iterate under RLock), so there is no snapshot to
+// invalidate.
+func removeHostInfo(list []*HostInfo, hi *HostInfo) []*HostInfo {
+	idx := slices.Index(list, hi)
+	if idx < 0 {
+		return list
+	}
+	return slices.Delete(list, idx, idx+1)
+}
+
+// DeleteHostInfo will fully unlink the hostinfo and return true if no other hostinfo still holds
+// any of its vpn addrs, meaning we no longer have a tunnel to the peer
 func (hm *HostMap) DeleteHostInfo(hostinfo *HostInfo) bool {
 	// Delete the host itself, ensuring it's not modified anymore
 	hm.Lock()
-	// If we have a previous or next hostinfo then we are not the last one for this vpn ip
-	final := (hostinfo.next == nil && hostinfo.prev == nil)
-	hm.unlockedDeleteHostInfo(hostinfo)
+	final := hm.unlockedDeleteHostInfo(hostinfo)
 	hm.Unlock()
 
 	return final
@@ -400,71 +453,69 @@ func (hm *HostMap) MakePrimary(hostinfo *HostInfo) {
 	hm.unlockedMakePrimary(hostinfo)
 }
 
-func (hm *HostMap) unlockedMakePrimary(hostinfo *HostInfo) {
-	// Get the current primary, if it exists
-	oldHostinfo := hm.Hosts[hostinfo.vpnAddrs[0]]
-
-	// Every address in the hostinfo gets elevated to primary
-	for _, vpnAddr := range hostinfo.vpnAddrs {
-		//NOTE: It is possible that we leave a dangling hostinfo here but connection manager works on
-		// indexes so it should be fine.
-		hm.Hosts[vpnAddr] = hostinfo
+// unlockedMakePrimary reports whether hostinfo is (now) the primary for each of its addresses,
+// false only when it is no longer in the hostmap at all.
+func (hm *HostMap) unlockedMakePrimary(hostinfo *HostInfo) bool {
+	// A hostinfo that is no longer in the hostmap must not be re-inserted here. Callers can race
+	// tunnel teardown, deciding to promote under the read lock and only taking the write lock
+	// after a delete fully unlinked the hostinfo (connection manager swapPrimary, AddRelay). Every
+	// live hostinfo is registered in Indexes by unlockedAddHostInfo, so this is a membership test.
+	if hm.Indexes[hostinfo.localIndexId] != hostinfo {
+		return false
 	}
 
-	// If we are already primary then we won't bother re-linking
-	if oldHostinfo == hostinfo {
-		return
-	}
-
-	// Unlink this hostinfo
-	if hostinfo.prev != nil {
-		hostinfo.prev.next = hostinfo.next
-	}
-	if hostinfo.next != nil {
-		hostinfo.next.prev = hostinfo.prev
-	}
-
-	// If there wasn't a previous primary then clear out any links
-	if oldHostinfo == nil {
-		hostinfo.next = nil
-		hostinfo.prev = nil
-		return
-	}
-
-	// Relink the hostinfo as primary
-	hostinfo.next = oldHostinfo
-	oldHostinfo.prev = hostinfo
-	hostinfo.prev = nil
-}
-
-func (hm *HostMap) unlockedDeleteHostInfo(hostinfo *HostInfo) {
-	isLastHostinfo := hostinfo.next == nil && hostinfo.prev == nil
-
+	// Move hostinfo to the front (primary) of each of its address lists. The lists are
+	// independent per address, so this can never leave a dangling entry the way promoting
+	// against a single shared chain could.
 	for _, addr := range hostinfo.vpnAddrs {
-		if hm.Hosts[addr] != hostinfo {
+		if hm.Hosts[addr] == hostinfo {
+			// Already primary for this address, the list is already in the right order
 			continue
 		}
-		if hostinfo.next != nil {
-			// Promote the next hostinfo in the shared chain to primary for this address
-			hm.Hosts[addr] = hostinfo.next
-		} else {
-			delete(hm.Hosts, addr)
+		list := removeHostInfo(hm.unlockedGetHostList(addr), hostinfo)
+		list = append([]*HostInfo{hostinfo}, list...)
+		hm.unlockedSetHostsForAddr(addr, list)
+	}
+	return true
+}
+
+// unlockedDeleteHostInfo removes hostinfo from every one of its address lists and from the index
+// maps. It returns true if this was the last hostinfo for all of its addresses (we no longer have
+// any tunnel to the peer), which the caller uses to decide whether to clear learned lighthouse
+// state and disestablish relays.
+func (hm *HostMap) unlockedDeleteHostInfo(hostinfo *HostInfo) bool {
+	// Lane sessions hang off this hostinfo, so deleting it takes them with it
+	// and there is nothing extra to unwind here.
+
+	// Remove this hostinfo from each of its address lists. The lists are independent, so a
+	// sibling is never promoted to an address it does not own and no other list is touched.
+	final := true
+	for _, addr := range hostinfo.vpnAddrs {
+		if list, ok := hm.moreHosts[addr]; ok {
+			list = removeHostInfo(list, hostinfo)
+			hm.unlockedSetHostsForAddr(addr, list)
+			if len(list) > 0 {
+				final = false
+			}
+		} else if existing, ok := hm.Hosts[addr]; ok {
+			if existing == hostinfo {
+				// Common case, the only hostinfo for this address. moreHosts has no entry to clean up.
+				delete(hm.Hosts, addr)
+			} else {
+				// We don't hold this address but another hostinfo does, we still have a tunnel to the peer
+				final = false
+			}
 		}
 	}
+
+	// Go maps never shrink their buckets, replace fully drained maps so a node that churned
+	// through a large peer count gives the memory back. Same idiom as the index maps below.
 	if len(hm.Hosts) == 0 {
 		hm.Hosts = map[netip.Addr]*HostInfo{}
 	}
-
-	// Splice this hostinfo out of the shared chain exactly once
-	if hostinfo.prev != nil {
-		hostinfo.prev.next = hostinfo.next
+	if len(hm.moreHosts) == 0 {
+		hm.moreHosts = map[netip.Addr][]*HostInfo{}
 	}
-	if hostinfo.next != nil {
-		hostinfo.next.prev = hostinfo.prev
-	}
-
-	hostinfo.next = nil
-	hostinfo.prev = nil
 
 	// The remote index uses index ids outside our control so lets make sure we are only removing
 	// the remote index pointer here if it points to the hostinfo we are deleting
@@ -488,7 +539,7 @@ func (hm *HostMap) unlockedDeleteHostInfo(hostinfo *HostInfo) {
 		)
 	}
 
-	if isLastHostinfo {
+	if final {
 		// I have lost connectivity to my peers. My relay tunnel is likely broken. Mark the next
 		// hops as 'Requested' so that new relay tunnels are created in the future.
 		hm.unlockedDisestablishVpnAddrRelayFor(hostinfo)
@@ -497,6 +548,19 @@ func (hm *HostMap) unlockedDeleteHostInfo(hostinfo *HostInfo) {
 	for _, localRelayIdx := range hostinfo.relayState.CopyRelayForIdxs() {
 		delete(hm.Relays, localRelayIdx)
 	}
+
+	return final
+}
+
+func (hm *HostMap) QueryIndexCached(index uint32, cache map[uint32]*HostInfo) *HostInfo {
+	if out, ok := cache[index]; ok {
+		return out
+	}
+	out := hm.QueryIndex(index)
+	if out != nil {
+		cache[index] = out
+	}
+	return out
 }
 
 func (hm *HostMap) QueryIndex(index uint32) *HostInfo {
@@ -540,19 +604,30 @@ func (hm *HostMap) QueryVpnAddrsRelayFor(targetIps []netip.Addr, relayHostIp net
 	hm.RLock()
 	defer hm.RUnlock()
 
+	// This runs per relayed packet, so check the primary with a single map probe and only consult
+	// moreHosts when the primary can't relay for us.
 	h, ok := hm.Hosts[relayHostIp]
 	if !ok {
 		return nil, nil, errors.New("unable to find host")
 	}
 
-	for h != nil {
-		for _, targetIp := range targetIps {
-			r, ok := h.relayState.QueryRelayForByIp(targetIp)
-			if ok && r.State == Established {
-				return h, r, nil
+	for _, targetIp := range targetIps {
+		r, ok := h.relayState.QueryRelayForByIp(targetIp)
+		if ok && r.State == Established {
+			return h, r, nil
+		}
+	}
+
+	if list, ok := hm.moreHosts[relayHostIp]; ok {
+		// list[0] is the primary we already checked
+		for _, h := range list[1:] {
+			for _, targetIp := range targetIps {
+				r, ok := h.relayState.QueryRelayForByIp(targetIp)
+				if ok && r.State == Established {
+					return h, r, nil
+				}
 			}
 		}
-		h = h.next
 	}
 
 	return nil, nil, errors.New("unable to find host with relay")
@@ -560,20 +635,14 @@ func (hm *HostMap) QueryVpnAddrsRelayFor(targetIps []netip.Addr, relayHostIp net
 
 func (hm *HostMap) unlockedDisestablishVpnAddrRelayFor(hi *HostInfo) {
 	for _, relayHostIp := range hi.relayState.CopyRelayIps() {
-		if h, ok := hm.Hosts[relayHostIp]; ok {
-			for h != nil {
-				h.relayState.UpdateRelayForByIpState(hi.vpnAddrs[0], Disestablished)
-				h = h.next
-			}
+		for _, h := range hm.unlockedGetHostList(relayHostIp) {
+			h.relayState.UpdateRelayForByIpState(hi.vpnAddrs[0], Disestablished)
 		}
 	}
 	for _, rs := range hi.relayState.CopyAllRelayFor() {
 		if rs.Type == ForwardingType {
-			if h, ok := hm.Hosts[rs.PeerAddr]; ok {
-				for h != nil {
-					h.relayState.UpdateRelayForByIpState(hi.vpnAddrs[0], Disestablished)
-					h = h.next
-				}
+			for _, h := range hm.unlockedGetHostList(rs.PeerAddr) {
+				h.relayState.UpdateRelayForByIpState(hi.vpnAddrs[0], Disestablished)
 			}
 		}
 	}
@@ -609,7 +678,7 @@ func (hm *HostMap) unlockedAddHostInfo(hostinfo *HostInfo, f *Interface) {
 	hm.Indexes[hostinfo.localIndexId] = hostinfo
 	hm.RemoteIndexes[hostinfo.remoteIndexId] = hostinfo
 
-	hostinfo.out.Store(true)
+	hostinfo.markOut(f.rebindEpoch.Load())
 	if f.connectionManager != nil { // f.connectionManager is only nil in some unit tests
 		f.connectionManager.trafficTimer.Add(hostinfo.localIndexId, f.connectionManager.checkInterval)
 	}
@@ -623,22 +692,27 @@ func (hm *HostMap) unlockedAddHostInfo(hostinfo *HostInfo, f *Interface) {
 }
 
 func (hm *HostMap) unlockedInnerAddHostInfo(vpnAddr netip.Addr, hostinfo *HostInfo, f *Interface) {
-	existing := hm.Hosts[vpnAddr]
-	hm.Hosts[vpnAddr] = hostinfo
-
-	if existing != nil && existing != hostinfo {
-		hostinfo.next = existing
-		existing.prev = hostinfo
+	existing, ok := hm.Hosts[vpnAddr]
+	if !ok {
+		// Common case, the first hostinfo for this address. moreHosts stays empty.
+		hm.Hosts[vpnAddr] = hostinfo
+		return
 	}
 
-	i := 1
-	check := hostinfo
-	for check != nil {
-		if i > MaxHostInfosPerVpnIp {
-			hm.unlockedDeleteHostInfo(check)
-		}
-		check = check.next
-		i++
+	// The new hostinfo becomes the primary for this address. Remove any stale copy of it first so
+	// we never hold a duplicate, then prepend.
+	list, ok := hm.moreHosts[vpnAddr]
+	if !ok {
+		list = []*HostInfo{existing}
+	}
+	list = removeHostInfo(list, hostinfo)
+	list = append([]*HostInfo{hostinfo}, list...)
+	hm.unlockedSetHostsForAddr(vpnAddr, list)
+
+	// Enforce the per-address cap by fully retiring the oldest hostinfo once we exceed it.
+	// Deleting it removes it from all of its addresses and the index maps, matching prior behavior.
+	if len(list) > MaxHostInfosPerVpnIp {
+		hm.unlockedDeleteHostInfo(list[len(list)-1])
 	}
 }
 
@@ -705,6 +779,64 @@ func (i *HostInfo) TryPromoteBest(preferredRanges []netip.Prefix, ifce *Interfac
 	}
 }
 
+// Bits within HostInfo.state, everything above stateEpochShift is the epoch
+const (
+	stateIn uint32 = 1 << iota
+	stateOut
+	statePendingDeletion
+
+	stateFlags = stateIn | stateOut | statePendingDeletion
+	// The epoch is the top 29 bits, it would take 2^29 rebinds to wrap and we will never get there
+	stateEpochShift = 3
+)
+
+// markIn records inbound traffic
+func (i *HostInfo) markIn() {
+	if i.state.Load()&stateIn == 0 {
+		i.state.Or(stateIn)
+	}
+}
+
+// markOut records a send and reports whether the epoch moved, meaning we want a punch from the far side
+func (i *HostInfo) markOut(epoch uint32) bool {
+	e := epoch << stateEpochShift
+	for {
+		old := i.state.Load()
+		if old&stateOut != 0 && old&^stateFlags == e {
+			return false
+		}
+
+		if i.state.CompareAndSwap(old, old&stateFlags|stateOut|e) {
+			return old&^stateFlags != e
+		}
+	}
+}
+
+// markOutOnly records a send without consuming the rebind epoch, for paths that cannot act on a requery
+func (i *HostInfo) markOutOnly() {
+	if i.state.Load()&stateOut == 0 {
+		i.state.Or(stateOut)
+	}
+}
+
+// takeTraffic clears both traffic bits, leaving the epoch alone, and reports what they were
+func (i *HostInfo) takeTraffic() (in bool, out bool) {
+	old := i.state.And(^(stateIn | stateOut))
+	return old&stateIn != 0, old&stateOut != 0
+}
+
+func (i *HostInfo) setPendingDeletion(v bool) {
+	if v {
+		i.state.Or(statePendingDeletion)
+	} else {
+		i.state.And(^statePendingDeletion)
+	}
+}
+
+func (i *HostInfo) isPendingDeletion() bool {
+	return i.state.Load()&statePendingDeletion != 0
+}
+
 func (i *HostInfo) GetCert() *cert.CachedCertificate {
 	if i.ConnectionState != nil {
 		return i.ConnectionState.peerCert

hostmap_test.go

@@ -2,6 +2,7 @@ package nebula
 
 import (
 	"net/netip"
+	"slices"
 	"testing"
 
 	"github.com/slackhq/nebula/config"
@@ -10,78 +11,84 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// chainIds returns the localIndexIds of the hostinfos holding addr, primary (index 0) first. It
+// also validates the Hosts/moreHosts sync contract on every call so a mutation that broke it
+// fails fast.
+func chainIds(t *testing.T, hm *HostMap, addr netip.Addr) []uint32 {
+	t.Helper()
+	assertHostMapInvariants(t, hm)
+	list := hm.unlockedGetHostList(addr)
+	ids := make([]uint32, len(list))
+	for i, h := range list {
+		ids[i] = h.localIndexId
+	}
+	return ids
+}
+
+// assertHostMapInvariants checks the Hosts/moreHosts contract: moreHosts only holds addresses
+// with 2 or more hostinfos, its first entry is always the primary in Hosts, lists never hold
+// duplicates, every hostinfo in a list owns the address and is registered in Indexes, and every
+// indexed hostinfo is reachable through each of its addresses.
+func assertHostMapInvariants(t *testing.T, hm *HostMap) {
+	t.Helper()
+	for addr, list := range hm.moreHosts {
+		require.GreaterOrEqualf(t, len(list), 2, "moreHosts[%s] must hold at least 2 hostinfos", addr)
+		require.Samef(t, hm.Hosts[addr], list[0], "moreHosts[%s][0] must match the primary in Hosts", addr)
+		seen := map[*HostInfo]bool{}
+		for _, h := range list {
+			require.NotNilf(t, h, "moreHosts[%s] must never hold a nil hostinfo", addr)
+			require.Falsef(t, seen[h], "moreHosts[%s] holds hostinfo %d twice", addr, h.localIndexId)
+			seen[h] = true
+			require.Samef(t, hm.Indexes[h.localIndexId], h, "moreHosts[%s] member %d is not registered in Indexes", addr, h.localIndexId)
+			require.Truef(t, slices.Contains(h.vpnAddrs, addr), "moreHosts[%s] member %d does not own the address", addr, h.localIndexId)
+		}
+	}
+	for addr, h := range hm.Hosts {
+		require.NotNilf(t, h, "Hosts[%s] must never be nil", addr)
+		require.Samef(t, hm.Indexes[h.localIndexId], h, "Hosts[%s] primary %d is not registered in Indexes", addr, h.localIndexId)
+		require.Truef(t, slices.Contains(h.vpnAddrs, addr), "Hosts[%s] primary (index %d) does not own the address", addr, h.localIndexId)
+	}
+	for idx, h := range hm.Indexes {
+		require.Equalf(t, idx, h.localIndexId, "Indexes[%d] holds hostinfo with localIndexId %d", idx, h.localIndexId)
+		for _, va := range h.vpnAddrs {
+			require.Truef(t, slices.Contains(hm.unlockedGetHostList(va), h), "indexed hostinfo %d is missing from the list for %s", idx, va)
+		}
+	}
+}
+
 func TestHostMap_MakePrimary(t *testing.T) {
 	l := test.NewLogger()
 	hm := newHostMap(l)
 
 	f := &Interface{}
+	a := netip.MustParseAddr("0.0.0.1")
 
-	h1 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 1}
-	h2 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 2}
-	h3 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 3}
-	h4 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 4}
+	h1 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 1}
+	h2 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 2}
+	h3 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 3}
+	h4 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 4}
 
 	hm.unlockedAddHostInfo(h4, f)
 	hm.unlockedAddHostInfo(h3, f)
 	hm.unlockedAddHostInfo(h2, f)
 	hm.unlockedAddHostInfo(h1, f)
 
-	// Make sure we go h1 -> h2 -> h3 -> h4
-	prim := hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h1.localIndexId, prim.localIndexId)
-	assert.Equal(t, h2.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h1.localIndexId, h2.prev.localIndexId)
-	assert.Equal(t, h3.localIndexId, h2.next.localIndexId)
-	assert.Equal(t, h2.localIndexId, h3.prev.localIndexId)
-	assert.Equal(t, h4.localIndexId, h3.next.localIndexId)
-	assert.Equal(t, h3.localIndexId, h4.prev.localIndexId)
-	assert.Nil(t, h4.next)
+	// Most-recently-added is primary: h1, h2, h3, h4
+	assert.Equal(t, []uint32{1, 2, 3, 4}, chainIds(t, hm, a))
+	assert.Equal(t, h1, hm.QueryVpnAddr(a))
 
-	// Swap h3/middle to primary
+	// Swap the middle to primary: h3, h1, h2, h4
 	hm.MakePrimary(h3)
+	assert.Equal(t, []uint32{3, 1, 2, 4}, chainIds(t, hm, a))
+	assert.Equal(t, h3, hm.QueryVpnAddr(a))
 
-	// Make sure we go h3 -> h1 -> h2 -> h4
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h3.localIndexId, prim.localIndexId)
-	assert.Equal(t, h1.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h2.localIndexId, h1.next.localIndexId)
-	assert.Equal(t, h3.localIndexId, h1.prev.localIndexId)
-	assert.Equal(t, h4.localIndexId, h2.next.localIndexId)
-	assert.Equal(t, h1.localIndexId, h2.prev.localIndexId)
-	assert.Equal(t, h2.localIndexId, h4.prev.localIndexId)
-	assert.Nil(t, h4.next)
-
-	// Swap h4/tail to primary
+	// Swap the tail to primary: h4, h3, h1, h2
 	hm.MakePrimary(h4)
+	assert.Equal(t, []uint32{4, 3, 1, 2}, chainIds(t, hm, a))
 
-	// Make sure we go h4 -> h3 -> h1 -> h2
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h4.localIndexId, prim.localIndexId)
-	assert.Equal(t, h3.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h1.localIndexId, h3.next.localIndexId)
-	assert.Equal(t, h4.localIndexId, h3.prev.localIndexId)
-	assert.Equal(t, h2.localIndexId, h1.next.localIndexId)
-	assert.Equal(t, h3.localIndexId, h1.prev.localIndexId)
-	assert.Equal(t, h1.localIndexId, h2.prev.localIndexId)
-	assert.Nil(t, h2.next)
-
-	// Swap h4 again should be no-op
+	// Swapping the current primary again is a no-op
 	hm.MakePrimary(h4)
-
-	// Make sure we go h4 -> h3 -> h1 -> h2
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h4.localIndexId, prim.localIndexId)
-	assert.Equal(t, h3.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h1.localIndexId, h3.next.localIndexId)
-	assert.Equal(t, h4.localIndexId, h3.prev.localIndexId)
-	assert.Equal(t, h2.localIndexId, h1.next.localIndexId)
-	assert.Equal(t, h3.localIndexId, h1.prev.localIndexId)
-	assert.Equal(t, h1.localIndexId, h2.prev.localIndexId)
-	assert.Nil(t, h2.next)
+	assert.Equal(t, []uint32{4, 3, 1, 2}, chainIds(t, hm, a))
 }
 
 func TestHostMap_DeleteHostInfo(t *testing.T) {
@@ -89,13 +96,14 @@ func TestHostMap_DeleteHostInfo(t *testing.T) {
 	hm := newHostMap(l)
 
 	f := &Interface{}
+	a := netip.MustParseAddr("0.0.0.1")
 
-	h1 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 1}
-	h2 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 2}
-	h3 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 3}
-	h4 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 4}
-	h5 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 5}
-	h6 := &HostInfo{vpnAddrs: []netip.Addr{netip.MustParseAddr("0.0.0.1")}, localIndexId: 6}
+	h1 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 1}
+	h2 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 2}
+	h3 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 3}
+	h4 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 4}
+	h5 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 5}
+	h6 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 6}
 
 	hm.unlockedAddHostInfo(h6, f)
 	hm.unlockedAddHostInfo(h5, f)
@@ -104,94 +112,110 @@ func TestHostMap_DeleteHostInfo(t *testing.T) {
 	hm.unlockedAddHostInfo(h2, f)
 	hm.unlockedAddHostInfo(h1, f)
 
-	// h6 should be deleted
-	assert.Nil(t, h6.next)
-	assert.Nil(t, h6.prev)
-	h := hm.QueryIndex(h6.localIndexId)
-	assert.Nil(t, h)
+	// h6 is evicted by the MaxHostInfosPerVpnIp cap; the rest are newest-first.
+	assert.Nil(t, hm.QueryIndex(h6.localIndexId))
+	assert.Equal(t, []uint32{1, 2, 3, 4, 5}, chainIds(t, hm, a))
 
-	// Make sure we go h1 -> h2 -> h3 -> h4 -> h5
-	prim := hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h1.localIndexId, prim.localIndexId)
-	assert.Equal(t, h2.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h1.localIndexId, h2.prev.localIndexId)
-	assert.Equal(t, h3.localIndexId, h2.next.localIndexId)
-	assert.Equal(t, h2.localIndexId, h3.prev.localIndexId)
-	assert.Equal(t, h4.localIndexId, h3.next.localIndexId)
-	assert.Equal(t, h3.localIndexId, h4.prev.localIndexId)
-	assert.Equal(t, h5.localIndexId, h4.next.localIndexId)
-	assert.Equal(t, h4.localIndexId, h5.prev.localIndexId)
-	assert.Nil(t, h5.next)
+	// Delete primary; not final since siblings remain.
+	assert.False(t, hm.DeleteHostInfo(h1))
+	assert.Equal(t, []uint32{2, 3, 4, 5}, chainIds(t, hm, a))
 
-	// Delete primary
-	hm.DeleteHostInfo(h1)
-	assert.Nil(t, h1.prev)
-	assert.Nil(t, h1.next)
+	// Deleting the same hostinfo again must not report final while siblings remain and must not
+	// disturb the list. The old chain code got this wrong: the first delete nil'd next/prev, so a
+	// second delete looked final and wiped lighthouse state out from under the live sibling.
+	assert.False(t, hm.DeleteHostInfo(h1))
+	assert.Equal(t, []uint32{2, 3, 4, 5}, chainIds(t, hm, a))
 
-	// Make sure we go h2 -> h3 -> h4 -> h5
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h2.localIndexId, prim.localIndexId)
-	assert.Equal(t, h3.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h3.localIndexId, h2.next.localIndexId)
-	assert.Equal(t, h2.localIndexId, h3.prev.localIndexId)
-	assert.Equal(t, h4.localIndexId, h3.next.localIndexId)
-	assert.Equal(t, h3.localIndexId, h4.prev.localIndexId)
-	assert.Equal(t, h5.localIndexId, h4.next.localIndexId)
-	assert.Equal(t, h4.localIndexId, h5.prev.localIndexId)
-	assert.Nil(t, h5.next)
+	// Delete a middle node.
+	assert.False(t, hm.DeleteHostInfo(h3))
+	assert.Equal(t, []uint32{2, 4, 5}, chainIds(t, hm, a))
 
-	// Delete in the middle
-	hm.DeleteHostInfo(h3)
-	assert.Nil(t, h3.prev)
-	assert.Nil(t, h3.next)
+	// Delete the tail.
+	assert.False(t, hm.DeleteHostInfo(h5))
+	assert.Equal(t, []uint32{2, 4}, chainIds(t, hm, a))
 
-	// Make sure we go h2 -> h4 -> h5
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h2.localIndexId, prim.localIndexId)
-	assert.Equal(t, h4.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h4.localIndexId, h2.next.localIndexId)
-	assert.Equal(t, h2.localIndexId, h4.prev.localIndexId)
-	assert.Equal(t, h5.localIndexId, h4.next.localIndexId)
-	assert.Equal(t, h4.localIndexId, h5.prev.localIndexId)
-	assert.Nil(t, h5.next)
+	// Delete the head; h4 remains and becomes primary.
+	assert.False(t, hm.DeleteHostInfo(h2))
+	assert.Equal(t, []uint32{4}, chainIds(t, hm, a))
+	assert.Equal(t, h4, hm.QueryVpnAddr(a))
 
-	// Delete the tail
-	hm.DeleteHostInfo(h5)
-	assert.Nil(t, h5.prev)
-	assert.Nil(t, h5.next)
+	// Delete the only remaining item; final is true and the address is gone.
+	assert.True(t, hm.DeleteHostInfo(h4))
+	assert.Empty(t, chainIds(t, hm, a))
+	assert.Nil(t, hm.QueryVpnAddr(a))
 
-	// Make sure we go h2 -> h4
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h2.localIndexId, prim.localIndexId)
-	assert.Equal(t, h4.localIndexId, prim.next.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Equal(t, h4.localIndexId, h2.next.localIndexId)
-	assert.Equal(t, h2.localIndexId, h4.prev.localIndexId)
-	assert.Nil(t, h4.next)
+	// Deleting an already-gone hostinfo is still final; nothing holds the address anymore.
+	assert.True(t, hm.DeleteHostInfo(h4))
+	assert.Empty(t, chainIds(t, hm, a))
+}
 
-	// Delete the head
-	hm.DeleteHostInfo(h2)
-	assert.Nil(t, h2.prev)
-	assert.Nil(t, h2.next)
+// TestHostMap_MakePrimary_DeletedHostInfo covers promoting a hostinfo that lost a race with
+// tunnel teardown: swapPrimary and AddRelay decide to promote while holding a stale pointer and
+// only take the write lock after a delete fully unlinked the hostinfo. MakePrimary must be a
+// no-op, not a resurrection that installs an unmanaged primary.
+func TestHostMap_MakePrimary_DeletedHostInfo(t *testing.T) {
+	l := test.NewLogger()
+	hm := newHostMap(l)
+	f := &Interface{}
+	a := netip.MustParseAddr("0.0.0.1")
 
-	// Make sure we only have h4
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Equal(t, h4.localIndexId, prim.localIndexId)
-	assert.Nil(t, prim.prev)
-	assert.Nil(t, prim.next)
-	assert.Nil(t, h4.next)
+	h1 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 1}
+	h2 := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 2}
+	hm.unlockedAddHostInfo(h1, f)
+	hm.unlockedAddHostInfo(h2, f)
 
-	// Delete the only item
-	hm.DeleteHostInfo(h4)
-	assert.Nil(t, h4.prev)
-	assert.Nil(t, h4.next)
+	// h1 is fully deleted while another goroutine still holds a pointer to it.
+	assert.False(t, hm.DeleteHostInfo(h1))
+	assert.Equal(t, []uint32{2}, chainIds(t, hm, a))
 
-	// Make sure we have nil
-	prim = hm.QueryVpnAddr(netip.MustParseAddr("0.0.0.1"))
-	assert.Nil(t, prim)
+	// The stale promote must not bring it back.
+	hm.MakePrimary(h1)
+	assert.Equal(t, []uint32{2}, chainIds(t, hm, a))
+	assert.Equal(t, h2, hm.QueryVpnAddr(a))
+	assert.Nil(t, hm.QueryIndex(h1.localIndexId))
+}
+
+// TestHostMap_QueryVpnAddrsRelayFor_NonPrimary makes sure a relay established on an older
+// hostinfo is still found after a newer tunnel without relay state takes primary for the same
+// address. The lookup checks the primary first and falls back to the rest of the list.
+func TestHostMap_QueryVpnAddrsRelayFor_NonPrimary(t *testing.T) {
+	l := test.NewLogger()
+	hm := newHostMap(l)
+	f := &Interface{}
+	relayAddr := netip.MustParseAddr("0.0.0.9")
+	target := netip.MustParseAddr("0.0.0.1")
+
+	older := &HostInfo{
+		vpnAddrs:     []netip.Addr{relayAddr},
+		localIndexId: 1,
+		relayState: RelayState{
+			relayForByAddr: map[netip.Addr]*Relay{},
+			relayForByIdx:  map[uint32]*Relay{},
+		},
+	}
+	older.relayState.InsertRelay(target, 100, &Relay{Type: ForwardingType, State: Established, LocalIndex: 100, PeerAddr: target})
+	hm.unlockedAddHostInfo(older, f)
+
+	// The relay is found on the primary.
+	h, r, err := hm.QueryVpnAddrsRelayFor([]netip.Addr{target}, relayAddr)
+	require.NoError(t, err)
+	assert.Equal(t, older, h)
+	assert.Equal(t, uint32(100), r.LocalIndex)
+
+	// A re-handshake with no relay state takes primary; the established relay on the older
+	// hostinfo must still be found through the fallback.
+	newer := &HostInfo{vpnAddrs: []netip.Addr{relayAddr}, localIndexId: 2}
+	hm.unlockedAddHostInfo(newer, f)
+	assert.Equal(t, []uint32{2, 1}, chainIds(t, hm, relayAddr))
+
+	h, r, err = hm.QueryVpnAddrsRelayFor([]netip.Addr{target}, relayAddr)
+	require.NoError(t, err)
+	assert.Equal(t, older, h)
+	assert.Equal(t, uint32(100), r.LocalIndex)
+
+	// No hostinfo at all is a plain miss.
+	_, _, err = hm.QueryVpnAddrsRelayFor([]netip.Addr{target}, netip.MustParseAddr("0.0.0.42"))
+	require.Error(t, err)
 }
 
 // TestHostMap_DeleteHostInfo_MultipleVpnAddrs exercises the case where a hostinfo carries more than one
@@ -216,32 +240,82 @@ func TestHostMap_DeleteHostInfo_MultipleVpnAddrs(t *testing.T) {
 	hm.unlockedAddHostInfo(other, f)
 	hm.unlockedAddHostInfo(head, f)
 
-	// head is primary for both addresses, other is next in the shared chain
-	assert.Equal(t, head.localIndexId, hm.QueryVpnAddr(a).localIndexId)
-	assert.Equal(t, head.localIndexId, hm.QueryVpnAddr(b).localIndexId)
-	assert.Equal(t, other.localIndexId, head.next.localIndexId)
-	assert.Equal(t, head.localIndexId, other.prev.localIndexId)
+	// head is primary for both addresses, other is next in each address's list.
+	assert.Equal(t, head, hm.QueryVpnAddr(a))
+	assert.Equal(t, head, hm.QueryVpnAddr(b))
+	assert.Equal(t, []uint32{2, 1}, chainIds(t, hm, a))
+	assert.Equal(t, []uint32{2, 1}, chainIds(t, hm, b))
 
 	// Delete the head. other is still live, so it must become primary for BOTH addresses.
-	hm.DeleteHostInfo(head)
+	assert.False(t, hm.DeleteHostInfo(head))
+	assert.Equal(t, other, hm.QueryVpnAddr(a))
+	assert.Equal(t, other, hm.QueryVpnAddr(b))
+	assert.Equal(t, []uint32{1}, chainIds(t, hm, a))
+	assert.Equal(t, []uint32{1}, chainIds(t, hm, b))
 
-	// Pre-fix: QueryVpnAddr(b) came back nil here because the second address was deleted rather than
-	// promoted, leaving other unreachable at b.
-	require.NotNil(t, hm.QueryVpnAddr(a))
-	require.NotNil(t, hm.QueryVpnAddr(b))
-	assert.Equal(t, other.localIndexId, hm.QueryVpnAddr(a).localIndexId)
-	assert.Equal(t, other.localIndexId, hm.QueryVpnAddr(b).localIndexId)
-
-	// other is now the only hostinfo in the chain
-	assert.Nil(t, other.prev)
-	assert.Nil(t, other.next)
-
-	// head is fully detached
-	assert.Nil(t, head.prev)
-	assert.Nil(t, head.next)
+	// head is fully removed from the index map.
 	assert.Nil(t, hm.QueryIndex(head.localIndexId))
 }
 
+// TestHostMap_DeleteHostInfo_DivergentVpnAddrs covers chained hostinfos for the same peer whose
+// vpnAddrs sets differ (a re-handshake cert added a second address). Deleting the superset node
+// must not promote a sibling to an address it does not own.
+func TestHostMap_DeleteHostInfo_DivergentVpnAddrs(t *testing.T) {
+	l := test.NewLogger()
+	hm := newHostMap(l)
+	f := &Interface{}
+	a := netip.MustParseAddr("0.0.0.1")
+	b := netip.MustParseAddr("0.0.0.2")
+
+	// sub owns only a; super (a newer handshake) owns a and b.
+	sub := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 1}
+	super := &HostInfo{vpnAddrs: []netip.Addr{a, b}, localIndexId: 2}
+	hm.unlockedAddHostInfo(sub, f)
+	hm.unlockedAddHostInfo(super, f)
+
+	assert.Equal(t, []uint32{2, 1}, chainIds(t, hm, a))
+	assert.Equal(t, []uint32{2}, chainIds(t, hm, b))
+
+	// Delete super: a promotes to sub (which owns it); b has no remaining owner and must be
+	// removed, not dangled at sub (which does not own b).
+	assert.False(t, hm.DeleteHostInfo(super))
+	assert.Equal(t, []uint32{1}, chainIds(t, hm, a))
+	assert.Empty(t, chainIds(t, hm, b))
+	assert.Equal(t, sub, hm.QueryVpnAddr(a))
+	assert.Nil(t, hm.QueryVpnAddr(b))
+	assert.Nil(t, hm.QueryIndex(super.localIndexId))
+
+	// Deleting sub cleans up fully.
+	assert.True(t, hm.DeleteHostInfo(sub))
+	assert.Nil(t, hm.QueryVpnAddr(a))
+	assertHostMapInvariants(t, hm)
+}
+
+// TestHostMap_AddDivergentOverlap covers a new hostinfo claiming addresses currently owned by two
+// DIFFERENT hostinfos. The old single shared next/prev chain overwrote a pointer and orphaned one
+// of them (in Indexes but unreachable via its address); independent per-address lists cannot.
+func TestHostMap_AddDivergentOverlap(t *testing.T) {
+	l := test.NewLogger()
+	hm := newHostMap(l)
+	f := &Interface{}
+	a := netip.MustParseAddr("0.0.0.1")
+	b := netip.MustParseAddr("0.0.0.2")
+
+	hiA := &HostInfo{vpnAddrs: []netip.Addr{a}, localIndexId: 1}
+	hiP := &HostInfo{vpnAddrs: []netip.Addr{b}, localIndexId: 2}
+	hm.unlockedAddHostInfo(hiA, f)
+	hm.unlockedAddHostInfo(hiP, f)
+
+	hiB := &HostInfo{vpnAddrs: []netip.Addr{a, b}, localIndexId: 3}
+	hm.unlockedAddHostInfo(hiB, f)
+
+	assert.Equal(t, []uint32{3, 1}, chainIds(t, hm, a))
+	assert.Equal(t, []uint32{3, 2}, chainIds(t, hm, b))
+	// hiA is still reachable via its address (not orphaned) and still indexed.
+	assert.Contains(t, chainIds(t, hm, a), hiA.localIndexId)
+	assert.NotNil(t, hm.QueryIndex(hiA.localIndexId))
+}
+
 // TestHostMap_MaxHostInfosPerVpnIp_MultipleVpnAddrs verifies the MaxHostInfosPerVpnIp overflow prune
 // (unlockedInnerAddHostInfo calls unlockedDeleteHostInfo on the oldest node once the chain is too long)
 // still behaves when hostinfos carry more than one vpnAddr. The pruned node is always the tail, so it is
@@ -267,32 +341,14 @@ func TestHostMap_MaxHostInfosPerVpnIp_MultipleVpnAddrs(t *testing.T) {
 
 	oldest := hostinfos[len(hostinfos)-1]
 
-	// The oldest hostinfo should have been pruned and fully detached
-	assert.Nil(t, oldest.next)
-	assert.Nil(t, oldest.prev)
+	// The oldest hostinfo was pruned from both lists and the index map.
 	assert.Nil(t, hm.QueryIndex(oldest.localIndexId))
 
-	// Both addresses resolve to the same head, and that head is one of the survivors (not the pruned one)
-	primA := hm.QueryVpnAddr(a)
-	primB := hm.QueryVpnAddr(b)
-	require.NotNil(t, primA)
-	require.NotNil(t, primB)
-	assert.Equal(t, primA.localIndexId, primB.localIndexId)
-	assert.NotEqual(t, oldest.localIndexId, primA.localIndexId)
-
-	// Walk the shared chain: exactly MaxHostInfosPerVpnIp survivors, no cycles, oldest absent
-	seen := map[uint32]struct{}{}
-	for h := primA; h != nil; h = h.next {
-		_, dup := seen[h.localIndexId]
-		require.False(t, dup, "cycle detected in hostinfo chain")
-		seen[h.localIndexId] = struct{}{}
-		if h.next != nil {
-			assert.Equal(t, h.localIndexId, h.next.prev.localIndexId, "prev pointer must mirror next")
-		}
-	}
-	assert.Len(t, seen, MaxHostInfosPerVpnIp)
-	_, prunedStillPresent := seen[oldest.localIndexId]
-	assert.False(t, prunedStillPresent)
+	// Both addresses hold exactly MaxHostInfosPerVpnIp survivors in the same order; oldest is absent.
+	require.Len(t, chainIds(t, hm, a), MaxHostInfosPerVpnIp)
+	assert.Equal(t, chainIds(t, hm, a), chainIds(t, hm, b), "both addresses must list the same survivors in the same order")
+	assert.NotContains(t, chainIds(t, hm, a), oldest.localIndexId)
+	assert.Equal(t, hm.QueryVpnAddr(a), hm.QueryVpnAddr(b))
 }
 
 func TestHostMap_reload(t *testing.T) {
@@ -345,3 +401,49 @@ func TestHostMap_RelayState(t *testing.T) {
 	assert.Equal(t, []netip.Addr{}, h1.relayState.relays)
 
 }
+
+// sentSinceCheck reports whether anything has been sent since the connection manager last looked. Test only:
+// production reads the out bit through takeTraffic on the connection manager tick.
+func (i *HostInfo) sentSinceCheck() bool {
+	return i.state.Load()&stateOut != 0
+}
+
+func TestHostInfo_markOut(t *testing.T) {
+	h := &HostInfo{}
+	h.markOut(5) // stamped when the tunnel was added
+
+	// A tunnel already on the current epoch has nothing to report, which is what keeps a fresh tunnel from
+	// requerying on its first packet
+	assert.False(t, h.markOut(5), "an unchanged epoch should not report a move")
+	assert.True(t, h.sentSinceCheck(), "the send is still recorded as traffic")
+
+	// A rebind is observed exactly once, so we requery once per rebind
+	assert.True(t, h.markOut(6), "a bumped epoch should report a move")
+	assert.False(t, h.markOut(6), "the epoch move should only be reported once")
+
+	// Traffic and pendingDeletion live in the same word and must survive an epoch change
+	h.setPendingDeletion(true)
+	h.markIn()
+	assert.True(t, h.markOut(7))
+	assert.True(t, h.isPendingDeletion(), "pendingDeletion must survive an epoch change")
+	in, out := h.takeTraffic()
+	assert.True(t, in, "inbound traffic must survive an epoch change")
+	assert.True(t, out)
+
+	// Clearing the traffic bits leaves the epoch alone, otherwise an idle tunnel would requery forever
+	assert.False(t, h.markOut(7), "takeTraffic must not disturb the epoch")
+}
+
+// A relayed send records traffic but must leave the rebind epoch for the direct path to consume, otherwise
+// relaying to a host swallows the requery that gets the far side punching at our new address.
+func TestHostInfo_markOutOnly(t *testing.T) {
+	h := &HostInfo{}
+	h.markOut(5)
+
+	h.markOutOnly()
+	assert.True(t, h.sentSinceCheck(), "a relayed send is still outbound traffic")
+	assert.False(t, h.markOut(5), "a relayed send must not disturb the epoch")
+
+	assert.True(t, h.markOut(6), "a relayed send must not consume the epoch edge")
+	assert.False(t, h.markOut(6))
+}

inside.go

@@ -2,6 +2,8 @@ package nebula
 
 import (
 	"context"
+	"fmt"
+	"io"
 	"log/slog"
 	"net/netip"
 
@@ -9,10 +11,23 @@ import (
 	"github.com/slackhq/nebula/header"
 	"github.com/slackhq/nebula/iputil"
 	"github.com/slackhq/nebula/noiseutil"
+	"github.com/slackhq/nebula/overlay/tio"
 	"github.com/slackhq/nebula/routing"
 )
 
-func (f *Interface) consumeInsidePacket(packet []byte, fwPacket *firewall.Packet, nb, out []byte, q int, localCache firewall.ConntrackCache) {
+func (f *Interface) consumeInsidePacket(pkt tio.Packet, fwPacket *firewall.ParsedPacket, nb []byte, tx *txQueue, rejectBuf []byte, q int, localCache firewall.ConntrackCache) {
+	// borrowed: pkt.Bytes is owned by the originating tio.Queue and is
+	// only valid until the next Read on that queue. Every consumer below
+	// (parse, self-forward, handshake cache, sendInsideMessage) reads it
+	// synchronously; do not retain pkt outside this call. If a future
+	// caller needs to keep the packet, use pkt.Clone() to detach it from
+	// the borrow.
+	//
+	// pkt.Bytes is either one IP datagram (GSO zero) or a TSO/USO
+	// superpacket. In both cases the L3+L4 headers at the start describe
+	// the same 5-tuple every segment will share, so a single newPacket /
+	// firewall check covers the whole superpacket.
+	packet := pkt.Bytes
 	err := newPacket(packet, false, fwPacket)
 	if err != nil {
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
@@ -37,7 +52,17 @@ func (f *Interface) consumeInsidePacket(packet []byte, fwPacket *firewall.Packet
 		// routes packets from the Nebula addr to the Nebula addr through the Nebula
 		// TUN device.
 		if immediatelyForwardToSelf {
-			_, err := f.readers[q].Write(packet)
+			// Write copies into the kernel queue synchronously, so seg's lifetime ends at return.
+			// A self-forwarded superpacket would be re-handed to the
+			// kernel as one giant blob; segment first so the loopback
+			// path sees one IP datagram per Write.
+			err := tio.SegmentSuperpacket(pkt, func(seg []byte) error {
+				// The kernel may have left the transport checksum for hardware
+				// offload to finish; nothing between here and the tun will.
+				iputil.SetTransportChecksum(seg)
+				_, werr := f.queues[q].Write(seg)
+				return werr
+			})
 			if err != nil {
 				f.l.Error("Failed to forward to tun", "error", err)
 			}
@@ -52,12 +77,24 @@ func (f *Interface) consumeInsidePacket(packet []byte, fwPacket *firewall.Packet
 		return
 	}
 
-	hostinfo, ready := f.getOrHandshakeConsiderRouting(fwPacket, func(hh *HandshakeHostInfo) {
-		hh.cachePacket(f.l, header.Message, 0, packet, f.sendMessageNow, f.cachedPacketMetrics)
+	hostinfo, ready := f.getOrHandshakeConsiderRouting(&fwPacket.Packet, func(hh *HandshakeHostInfo) {
+		// borrowed: SegmentSuperpacket builds each segment in the kernel-supplied pkt
+		// bytes underneath. cachePacket explicitly copies its argument (handshake_manager.go cachePacket),
+		// so retaining segments past the loop is safe.
+		err := tio.SegmentSuperpacket(pkt, func(seg []byte) error {
+			hh.cachePacket(f.l, header.Message, 0, seg, f.sendMessageNow, f.cachedPacketMetrics)
+			return nil
+		})
+		if err != nil && f.l.Enabled(context.Background(), slog.LevelDebug) {
+			f.l.Debug("Failed to segment superpacket for handshake cache",
+				"error", err,
+				"vpnAddr", fwPacket.RemoteAddr,
+			)
+		}
 	})
 
 	if hostinfo == nil {
-		f.rejectInside(packet, out, q)
+		f.rejectInside(packet, rejectBuf, q)
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
 			f.l.Debug("dropping outbound packet, vpnAddr not in our vpn networks or in unsafe networks",
 				"vpnAddr", fwPacket.RemoteAddr,
@@ -71,12 +108,11 @@ func (f *Interface) consumeInsidePacket(packet []byte, fwPacket *firewall.Packet
 		return
 	}
 
-	dropReason := f.firewall.Drop(*fwPacket, false, hostinfo, f.pki.GetCAPool(), localCache)
+	dropReason := f.firewall.Drop(fwPacket.Packet, false, hostinfo, f.pki.GetCAPool(), localCache)
 	if dropReason == nil {
-		f.sendNoMetrics(header.Message, 0, hostinfo.ConnectionState, hostinfo, netip.AddrPort{}, packet, nb, out, q)
-
+		f.sendInsideMessage(hostinfo, pkt, &fwPacket.Packet, nb, tx)
 	} else {
-		f.rejectInside(packet, out, q)
+		f.rejectInside(packet, rejectBuf, q)
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
 			hostinfo.logger(f.l).Debug("dropping outbound packet",
 				"fwPacket", fwPacket,
@@ -86,8 +122,148 @@ func (f *Interface) consumeInsidePacket(packet []byte, fwPacket *firewall.Packet
 	}
 }
 
+func (f *Interface) sendInsideEncrypt(hostinfo *HostInfo, ci *ConnectionState, lane uint8, seg, scratch, nb []byte) []byte {
+	if noiseutil.EncryptLockNeeded {
+		ci.writeLock.Lock()
+	}
+	c := ci.messageCounter.Add(1)
+
+	out := header.EncodeLane(scratch, header.Version, header.Message, 0, hostinfo.remoteIndexId, c, lane)
+
+	out, encErr := ci.eKey.EncryptDanger(out, out, seg, c, nb)
+	if noiseutil.EncryptLockNeeded {
+		ci.writeLock.Unlock()
+	}
+	if encErr != nil {
+		hostinfo.logger(f.l).Error("Failed to encrypt outgoing packet",
+			"error", encErr,
+			"udpAddr", hostinfo.GetRemote(),
+			"counter", c,
+		)
+		// Skip this segment; the rest of the superpacket can still go out. TCP will retransmit anything we drop here.
+		return nil
+	}
+
+	return out
+}
+
+// sendInsideMessage encrypts a firewall-approved inside packet (or every
+// segment of a TSO/USO superpacket) into the caller's batch slot for
+// later sendmmsg flush. Segmentation is fused with encryption here so the
+// kernel-supplied superpacket bytes never get written into a separate
+// scratch arena: SegmentSuperpacket builds each segment's plaintext in
+// segScratch[:segLen] in turn, and we encrypt directly into a fresh SendBatch slot.
+//
+// When this flow has a usable multiport lane to this peer, the direct path swaps
+// to that lane's session and socket below. Relay and base traffic stays on
+// tx.base (socket 0).
+func (f *Interface) sendInsideMessage(hostinfo *HostInfo, pkt tio.Packet, fwPacket *firewall.Packet, nb []byte, tx *txQueue) {
+	ci := hostinfo.ConnectionState
+	if ci.eKey == nil {
+		return
+	}
+
+	// Base and relay traffic stays on socket 0; the direct path may swap to tx.lane below.
+	sendBatch := tx.base
+
+	// One traffic-out mark covers every segment of the superpacket; doing it
+	// per segment in sendInsideEncrypt paid an atomic store up to ~45 extra
+	// times per TSO packet, inside writeLock under boring crypto.
+	//
+	// We rebound since this tunnel last sent, ask the lighthouse to get the far side punching at us again
+	if f.connectionManager.Out(hostinfo) {
+		f.lightHouse.QueryServer(hostinfo.vpnAddrs[0])
+		if f.l.Enabled(context.Background(), slog.LevelDebug) {
+			hostinfo.logger(f.l).Debug("Lighthouse update triggered for punch due to rebind epoch",
+				"vpnAddrs", hostinfo.vpnAddrs,
+			)
+		}
+	}
+
+	remote := hostinfo.GetRemote()
+	if !remote.IsValid() { //the relay path
+		//first, find our relay hostinfo:
+		var relayHostInfo *HostInfo
+		var relay *Relay
+		var err error
+		for _, relayIP := range hostinfo.relayState.CopyRelayIps() {
+			relayHostInfo, relay, err = f.hostMap.QueryVpnAddrsRelayFor(hostinfo.vpnAddrs, relayIP)
+			if err != nil {
+				hostinfo.relayState.DeleteRelay(relayIP)
+				hostinfo.logger(f.l).Info("sendNoMetrics failed to find HostInfo",
+					"relay", relayIP,
+					"error", err,
+				)
+				continue
+			}
+			break
+		}
+		if relayHostInfo == nil || relay == nil {
+			//failure already logged
+			return
+		}
+
+		err = tio.SegmentSuperpacket(pkt, func(seg []byte) error {
+			//relay header + header + plaintext + AEAD tag (16 bytes for both AES-GCM and ChaCha20-Poly1305) + relay tag
+			scratch := sendBatch.Reserve(header.Len + header.Len + len(seg) + 16 + 16)
+
+			innerPacket := f.sendInsideEncrypt(hostinfo, ci, 0, seg, scratch[header.Len:], nb)
+			if innerPacket == nil {
+				return nil
+			}
+
+			//now we need to do a relay-encrypt:
+			toSend, err := f.prepareSendVia(relayHostInfo, relay, innerPacket, nb, scratch, true)
+			if err != nil {
+				//already logged
+				return nil
+			}
+
+			sendBatch.Commit(toSend, relayHostInfo.GetRemote())
+			return nil
+		})
+		if err != nil {
+			hostinfo.logger(f.l).Error("Failed to segment superpacket for relay send", "error", err)
+		}
+		return
+	}
+
+	// Direct path: prefer this flow's multiport lane once it is proven usable.
+	// txLaneForFlow hands back the lane's session and destination together, so
+	// there is no window where one is set and the other is not, and a demotion
+	// drops us back onto the base tunnel on the very next packet.
+	//
+	// A miss is also how a lane gets re-probed after a demotion: txLane raises
+	// demand, which the connection manager's next tick on this tunnel picks up.
+	// Until the lane is up the traffic rides the base tunnel, the same fallback
+	// a demoted lane uses.
+	lane := uint8(0)
+	if s, lci, laneRemote := hostinfo.lanes.txLaneForFlow(fwPacket); lci != nil {
+		lane = uint8(s)
+		ci = lci
+		remote = laneRemote
+		sendBatch = tx.laneBatch(f, s)
+	}
+
+	err := tio.SegmentSuperpacket(pkt, func(seg []byte) error {
+		// header + plaintext + AEAD tag (16 bytes for both AES-GCM and ChaCha20-Poly1305)
+		scratch := sendBatch.Reserve(header.Len + len(seg) + 16)
+
+		out := f.sendInsideEncrypt(hostinfo, ci, lane, seg, scratch, nb)
+		if out == nil {
+			return nil
+		}
+
+		sendBatch.Commit(out, remote)
+		return nil
+	})
+	if err != nil {
+		hostinfo.logger(f.l).Error("Failed to segment superpacket for send", "error", err)
+	}
+}
+
 func (f *Interface) rejectInside(packet []byte, out []byte, q int) {
-	if !f.firewall.InSendReject {
+	if !f.firewall.OutboundSendReject {
 		return
 	}
 
@@ -96,33 +272,36 @@ func (f *Interface) rejectInside(packet []byte, out []byte, q int) {
 		return
 	}
 
-	_, err := f.readers[q].Write(out)
+	_, err := f.queues[q].Write(out)
 	if err != nil {
 		f.l.Error("Failed to write to tun", "error", err)
 	}
 }
 
-func (f *Interface) rejectOutside(packet []byte, ci *ConnectionState, hostinfo *HostInfo, nb, out []byte, q int) {
-	if !f.firewall.OutSendReject {
+func (f *Interface) rejectOutside(packet []byte, ci *ConnectionState, hostinfo *HostInfo, nb, rejectBuf []byte, q int) {
+	if !f.firewall.InboundSendReject {
 		return
 	}
 
-	out = iputil.CreateRejectPacket(packet, out)
+	// split rejectBuf to make sure we have room to write the plaintext rejection, then encrypt it, without trampling anything
+	// we can't re-use packet, if we need to send an icmp reject, it won't be long enough.
+	half := len(rejectBuf) / 2
+	encryptBuf := rejectBuf[0:0:half] //the first half of rejectBuf's capacity, len set to 0
+	buildBuf := rejectBuf[half:]
+
+	out := iputil.CreateRejectPacket(packet, buildBuf)
 	if len(out) == 0 {
 		return
 	}
 
 	if len(out) > iputil.MaxRejectPacketSize {
 		if f.l.Enabled(context.Background(), slog.LevelInfo) {
-			f.l.Info("rejectOutside: packet too big, not sending",
-				"packet", packet,
-				"outPacket", out,
-			)
+			f.l.Info("rejectOutside: packet too big, not sending", "packet", packet, "outPacket", out)
 		}
 		return
 	}
 
-	f.sendNoMetrics(header.Message, 0, ci, hostinfo, netip.AddrPort{}, out, nb, packet, q)
+	f.sendNoMetrics(header.Message, 0, ci, hostinfo, netip.AddrPort{}, out, nb, encryptBuf, q)
 }
 
 // Handshake will attempt to initiate a tunnel with the provided vpn address. This is a no-op if the tunnel is already established or being established
@@ -216,7 +395,7 @@ func (f *Interface) getOrHandshakeConsiderRouting(fwPacket *firewall.Packet, cac
 }
 
 func (f *Interface) sendMessageNow(t header.MessageType, st header.MessageSubType, hostinfo *HostInfo, p, nb, out []byte) {
-	fp := &firewall.Packet{}
+	fp := &firewall.ParsedPacket{}
 	err := newPacket(p, false, fp)
 	if err != nil {
 		f.l.Warn("error while parsing outgoing packet for firewall check", "error", err)
@@ -224,7 +403,7 @@ func (f *Interface) sendMessageNow(t header.MessageType, st header.MessageSubTyp
 	}
 
 	// check if packet is in outbound fw rules
-	dropReason := f.firewall.Drop(*fp, false, hostinfo, f.pki.GetCAPool(), nil)
+	dropReason := f.firewall.Drop(fp.Packet, false, hostinfo, f.pki.GetCAPool(), nil)
 	if dropReason != nil {
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
 			f.l.Debug("dropping cached packet",
@@ -275,29 +454,36 @@ func (f *Interface) sendTo(t header.MessageType, st header.MessageSubType, ci *C
 	f.sendNoMetrics(t, st, ci, hostinfo, remote, p, nb, out, 0)
 }
 
-// SendVia sends a payload through a Relay tunnel. No authentication or encryption is done
-// to the payload for the ultimate target host, making this a useful method for sending
-// handshake messages to peers through relay tunnels.
-// via is the HostInfo through which the message is relayed.
-// ad is the plaintext data to authenticate, but not encrypt
-// nb is a buffer used to store the nonce value, re-used for performance reasons.
-// out is a buffer used to store the result of the Encrypt operation
-// q indicates which writer to use to send the packet.
-func (f *Interface) SendVia(via *HostInfo,
+// dropExhausted records an exhaustion drop and logs once, on the crossing send, for a spent tunnel.
+func (f *Interface) dropExhausted(hostinfo *HostInfo, c uint64, msg string) {
+	f.messageMetrics.TxExhausted(1)
+	if c == RejectAfterMessages {
+		hostinfo.logger(f.l).Error(msg)
+	}
+}
+
+func (f *Interface) prepareSendVia(via *HostInfo,
 	relay *Relay,
 	ad,
 	nb,
 	out []byte,
 	nocopy bool,
-) {
+) ([]byte, error) {
 	if noiseutil.EncryptLockNeeded {
 		// NOTE: for goboring AESGCMTLS we need to lock because of the nonce check
 		via.ConnectionState.writeLock.Lock()
 	}
-	c := via.ConnectionState.messageCounter.Add(1)
+	c, ok := via.ConnectionState.NextMessageCounter()
+	if !ok {
+		if noiseutil.EncryptLockNeeded {
+			via.ConnectionState.writeLock.Unlock()
+		}
+		f.dropExhausted(via, c, "Dropping outbound relay packets, tunnel message counter is exhausted")
+		return nil, fmt.Errorf("tunnel message counter is exhausted")
+	}
 
 	out = header.Encode(out, header.Version, header.Message, header.MessageRelay, relay.RemoteIndex, c)
-	f.connectionManager.Out(via)
+	f.connectionManager.OutNoRebind(via)
 
 	// Authenticate the header and payload, but do not encrypt for this message type.
 	// The payload consists of the inner, unencrypted Nebula header, as well as the end-to-end encrypted payload.
@@ -311,7 +497,7 @@ func (f *Interface) SendVia(via *HostInfo,
 			"headerLen", len(out),
 			"cipherOverhead", via.ConnectionState.eKey.Overhead(),
 		)
-		return
+		return nil, io.ErrShortBuffer
 	}
 
 	// The header bytes are written to the 'out' slice; Grow the slice to hold the header and associated data payload.
@@ -331,19 +517,71 @@ func (f *Interface) SendVia(via *HostInfo,
 	}
 	if err != nil {
 		via.logger(f.l).Info("Failed to EncryptDanger in sendVia", "error", err)
+		return nil, err
+	}
+	f.connectionManager.RelayUsed(relay.LocalIndex)
+	return out, nil
+}
+
+// SendVia sends a payload through a Relay tunnel. No authentication or encryption is done
+// to the payload for the ultimate target host, making this a useful method for sending
+// handshake messages to peers through relay tunnels.
+// via is the HostInfo through which the message is relayed.
+// ad is the plaintext data to authenticate, but not encrypt
+// nb is a buffer used to store the nonce value, re-used for performance reasons.
+// out is a buffer used to store the result of the Encrypt operation
+// q indicates which writer to use to send the packet.
+func (f *Interface) SendVia(via *HostInfo, relay *Relay, ad, nb, out []byte, nocopy bool, q int) {
+	toSend, err := f.prepareSendVia(via, relay, ad, nb, out, nocopy)
+	if err != nil {
+		// already logged by prepareSendVia
 		return
 	}
-	err = f.writers[0].WriteTo(out, via.GetRemote())
+
+	err = f.writers[f.egressSock(q)].WriteTo(toSend, via.GetRemote())
 	if err != nil {
 		via.logger(f.l).Info("Failed to WriteTo in sendVia", "error", err)
 	}
-	f.connectionManager.RelayUsed(relay.LocalIndex)
+}
+
+// egressSock picks the socket a tunnel packet leaves from.
+//
+// Everything that is not lane data plane leaves from the base port: handshakes, keepalives, close packets, rejects and
+// relay carriers all belong to the base tunnel's 4-tuple, which is the only one a peer's spoof/roam checks and a
+// vanilla peer's expectations know about. Lane data goes through laneSock instead and never comes here.
+//
+// Which socket on the base port doesn't matter — they share an address, so they produce identical packets — so keep to
+// this routine's own share of the group and leave the rest of it uncontended. Without multiport that is q itself, since
+// every socket is on the base port.
+func (f *Interface) egressSock(q int) int {
+	return f.laneSock(q, 0)
+}
+
+// laneSock returns the index in writers of a socket bound to lane s's port, for a
+// routine that reads queue q.
+//
+// Under multiport the sockets are laid out port-major — writers[s*routinesPerPort
+// + r] is the r'th socket on port listen.port+s — so every routine has a sibling
+// socket on every port and the arithmetic is a lane index away. Routines pick the
+// sibling matching their own position in their group, which spreads the writers
+// for one port over that port's whole group rather than funnelling them onto its
+// first socket. It is a pure function of (q, s), so a flow always leaves from the
+// same socket and cannot reorder itself across two of them.
+//
+// Without multiport there is one port and every socket is on it, so any lane
+// resolves to q's own socket.
+func (f *Interface) laneSock(q, s int) int {
+	if !f.multiport {
+		return q
+	}
+	return s*f.routinesPerPort + q%f.routinesPerPort
 }
 
 func (f *Interface) sendNoMetrics(t header.MessageType, st header.MessageSubType, ci *ConnectionState, hostinfo *HostInfo, remote netip.AddrPort, p, nb, out []byte, q int) {
 	if ci.eKey == nil {
 		return
 	}
+	q = f.egressSock(q)
 	useRelay := !remote.IsValid() && !hostinfo.GetRemote().IsValid()
 	fullOut := out
 
@@ -361,21 +599,24 @@ func (f *Interface) sendNoMetrics(t header.MessageType, st header.MessageSubType
 		// NOTE: for goboring AESGCMTLS we need to lock because of the nonce check
 		ci.writeLock.Lock()
 	}
-	c := ci.messageCounter.Add(1)
+	c, ok := ci.NextMessageCounter()
+	if !ok {
+		if noiseutil.EncryptLockNeeded {
+			ci.writeLock.Unlock()
+		}
+		f.dropExhausted(hostinfo, c, "Dropping outbound packets, tunnel message counter is exhausted")
+		return
+	}
 
 	//l.WithField("trace", string(debug.Stack())).Error("out Header ", &Header{Version, t, st, 0, hostinfo.remoteIndexId, c}, p)
 	out = header.Encode(out, header.Version, t, st, hostinfo.remoteIndexId, c)
-	f.connectionManager.Out(hostinfo)
-
-	// Query our LH if we haven't since the last time we've been rebound, this will cause the remote to punch against
-	// all our addrs and enable a faster roaming.
-	if t != header.CloseTunnel && hostinfo.lastRebindCount != f.rebindCount {
-		//NOTE: there is an update hole if a tunnel isn't used and exactly 256 rebinds occur before the tunnel is
-		// finally used again. This tunnel would eventually be torn down and recreated if this action didn't help.
+	// A closing tunnel is torn down right after this, so skip the connection manager entirely: no point recording
+	// traffic or asking the lighthouse for a punch. Otherwise, if we rebound since this tunnel last sent, ask the
+	// lighthouse to get the far side punching at us again.
+	if t != header.CloseTunnel && f.connectionManager.Out(hostinfo) {
 		f.lightHouse.QueryServer(hostinfo.vpnAddrs[0])
-		hostinfo.lastRebindCount = f.rebindCount
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
-			f.l.Debug("Lighthouse update triggered for punch due to rebind counter",
+			f.l.Debug("Lighthouse update triggered for punch due to rebind epoch",
 				"vpnAddrs", hostinfo.vpnAddrs,
 			)
 		}
@@ -408,7 +649,7 @@ func (f *Interface) sendNoMetrics(t header.MessageType, st header.MessageSubType
 		if err != nil {
 			hostinfo.logger(f.l).Error("Failed to write outgoing packet",
 				"error", err,
-				"udpAddr", remote,
+				"udpAddr", hr,
 			)
 		}
 	} else {
@@ -423,7 +664,7 @@ func (f *Interface) sendNoMetrics(t header.MessageType, st header.MessageSubType
 				)
 				continue
 			}
-			f.SendVia(relayHostInfo, relay, out, nb, fullOut[:header.Len+len(out)], true)
+			f.SendVia(relayHostInfo, relay, out, nb, fullOut[:header.Len+len(out)], true, q)
 			break
 		}
 	}

inside_test.go

@@ -0,0 +1,265 @@
+package nebula
+
+import (
+	"encoding/binary"
+	"io"
+	"net/netip"
+	"testing"
+
+	"github.com/gaissmai/bart"
+	"github.com/slackhq/nebula/firewall"
+	"github.com/slackhq/nebula/iputil"
+	"github.com/slackhq/nebula/overlay/tio"
+	"github.com/slackhq/nebula/test"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	ipv4HeaderLen = 20
+	ipv6HeaderLen = 40
+)
+
+// capturingTun is a tio.Queue that records what is written to it. A queue that
+// discards writes is indistinguishable from a packet that was never forwarded.
+type capturingTun struct {
+	writes [][]byte
+}
+
+func (c *capturingTun) Read() ([]tio.Packet, error) { return nil, io.EOF }
+func (c *capturingTun) Close() error                { return nil }
+
+func (c *capturingTun) Write(b []byte) (int, error) {
+	c.writes = append(c.writes, append([]byte(nil), b...))
+	return len(b), nil
+}
+
+func newSelfForwardInterface(myAddrs ...netip.Addr) (*Interface, *capturingTun) {
+	vpnAddrs := &bart.Lite{}
+	for _, a := range myAddrs {
+		vpnAddrs.Insert(netip.PrefixFrom(a, a.BitLen()))
+	}
+
+	tun := &capturingTun{}
+	return &Interface{
+		l:                     test.NewLogger(),
+		myVpnAddrsTable:       vpnAddrs,
+		myBroadcastAddrsTable: &bart.Lite{},
+		queues:                []tio.Queue{tun},
+	}, tun
+}
+
+func consumeInside(f *Interface, packet []byte) {
+	f.consumeInsidePacket(tio.Packet{Bytes: packet}, &firewall.ParsedPacket{}, make([]byte, 12), nil, make([]byte, mtu), 0, nil)
+}
+
+// l4Proto describes one upper-layer header for these tests: its IP next-header
+// value, where its checksum field sits within the header, and how to build a
+// minimal instance of it.
+type l4Proto struct {
+	name    string
+	nextHdr uint8
+	cksumAt int
+	build   func() []byte
+}
+
+var (
+	tcpSyn = l4Proto{"tcp", iputil.IPProtocolTCP, 16, func() []byte {
+		h := make([]byte, 20)
+		binary.BigEndian.PutUint16(h[0:2], 49152)
+		binary.BigEndian.PutUint16(h[2:4], 443)
+		binary.BigEndian.PutUint32(h[4:8], 0x11223344) // sequence
+		h[12] = 5 << 4                                 // data offset, no options
+		h[13] = 0x02                                   // SYN
+		binary.BigEndian.PutUint16(h[14:16], 65535)    // window
+		return h
+	}}
+
+	udpDatagram = l4Proto{"udp", iputil.IPProtocolUDP, 6, func() []byte {
+		h := make([]byte, 8+4)
+		binary.BigEndian.PutUint16(h[0:2], 49152)
+		binary.BigEndian.PutUint16(h[2:4], 53)
+		binary.BigEndian.PutUint16(h[4:6], uint16(len(h)))
+		copy(h[8:], "ping")
+		return h
+	}}
+
+	icmpEcho   = l4Proto{"icmp", iputil.IPProtocolICMP, 2, func() []byte { return echoRequest(8) }}
+	icmpv6Echo = l4Proto{"icmpv6", iputil.IPProtocolICMPv6, 2, func() []byte { return echoRequest(128) }}
+)
+
+// echoRequest builds an echo request body. The type differs between ICMP and
+// ICMPv6, the rest of the header does not.
+func echoRequest(typ uint8) []byte {
+	h := make([]byte, 8)
+	h[0] = typ
+	binary.BigEndian.PutUint16(h[4:6], 0xbeef) // identifier
+	binary.BigEndian.PutUint16(h[6:8], 1)      // sequence
+	return h
+}
+
+func buildIPv6(src, dst netip.Addr, p l4Proto) []byte {
+	l4 := p.build()
+	pkt := make([]byte, ipv6HeaderLen+len(l4))
+	pkt[0] = 0x60
+	binary.BigEndian.PutUint16(pkt[4:6], uint16(len(l4)))
+	pkt[6] = p.nextHdr
+	pkt[7] = 64
+	copy(pkt[8:24], src.AsSlice())
+	copy(pkt[24:40], dst.AsSlice())
+	copy(pkt[ipv6HeaderLen:], l4)
+	if l4 := pkt[ipv6HeaderLen:]; p.nextHdr == iputil.IPProtocolTCP || p.nextHdr == iputil.IPProtocolUDP {
+		sum := ipv6PseudoheaderSum(src, dst, uint32(p.nextHdr), uint32(len(l4)))
+		binary.BigEndian.PutUint16(l4[p.cksumAt:], ^fold(sumBytes(l4, sum)))
+	}
+	return pkt
+}
+
+func buildIPv4(src, dst netip.Addr, p l4Proto) []byte {
+	l4 := p.build()
+	pkt := make([]byte, ipv4HeaderLen+len(l4))
+	pkt[0] = 0x45
+	binary.BigEndian.PutUint16(pkt[2:4], uint16(len(pkt)))
+	pkt[8] = 64
+	pkt[9] = p.nextHdr
+	copy(pkt[12:16], src.AsSlice())
+	copy(pkt[16:20], dst.AsSlice())
+	copy(pkt[ipv4HeaderLen:], l4)
+	if l4 := pkt[ipv4HeaderLen:]; p.nextHdr == iputil.IPProtocolTCP || p.nextHdr == iputil.IPProtocolUDP {
+		sum := sumBytes(pkt[12:20], uint32(p.nextHdr)+uint32(len(l4)))
+		binary.BigEndian.PutUint16(l4[p.cksumAt:], ^fold(sumBytes(l4, sum)))
+	}
+	return pkt
+}
+
+// ipv6PseudoheaderSum is the RFC 2460 section 8.1 pseudo-header sum: source,
+// destination, a 32 bit upper-layer packet length and a 32 bit zero-padded next
+// header. Kept local to the test so these assertions do not check nebula's
+// checksum code against itself.
+func ipv6PseudoheaderSum(src, dst netip.Addr, nextHeader, length uint32) uint32 {
+	var csum uint32
+	s, d := src.AsSlice(), dst.AsSlice()
+	for i := 0; i < 16; i += 2 {
+		csum += uint32(s[i])<<8 | uint32(s[i+1])
+		csum += uint32(d[i])<<8 | uint32(d[i+1])
+	}
+	return csum + length + nextHeader
+}
+
+func sumBytes(b []byte, csum uint32) uint32 {
+	for i := 0; i+1 < len(b); i += 2 {
+		csum += uint32(b[i])<<8 | uint32(b[i+1])
+	}
+	if len(b)%2 == 1 {
+		csum += uint32(b[len(b)-1]) << 8
+	}
+	return csum
+}
+
+func fold(csum uint32) uint16 {
+	for csum > 0xffff {
+		csum = (csum >> 16) + (csum & 0xffff)
+	}
+	return uint16(csum)
+}
+
+// l4ChecksumValid6 verifies an IPv6 upper-layer checksum the way a receiver
+// does: the pseudo-header plus the whole upper-layer segment, checksum field
+// included, folds to 0xffff. The next header field is the upper-layer protocol
+// only while there are no extension headers, which is all this file builds.
+func l4ChecksumValid6(pkt []byte) bool {
+	src, _ := netip.AddrFromSlice(pkt[8:24])
+	dst, _ := netip.AddrFromSlice(pkt[24:40])
+	l4 := pkt[ipv6HeaderLen:]
+	return fold(sumBytes(l4, ipv6PseudoheaderSum(src, dst, uint32(pkt[6]), uint32(len(l4))))) == 0xffff
+}
+
+// l4ChecksumValid4 is the IPv4 counterpart: the RFC 793/768 pseudo-header is
+// source, destination, a zero byte, the protocol and the upper-layer length.
+func l4ChecksumValid4(pkt []byte) bool {
+	ihl := int(pkt[0]&0x0f) << 2
+	l4 := pkt[ihl:]
+	return fold(sumBytes(l4, sumBytes(pkt[12:20], uint32(pkt[9])+uint32(len(l4))))) == 0xffff
+}
+
+// TestConsumeInsidePacketSelfTraffic covers the self-addressed branch of
+// consumeInsidePacket, taken where immediatelyForwardToSelf is set (see
+// inside_bsd.go): the packet goes straight back to the tun, ahead of the
+// firewall and the handshake.
+func TestConsumeInsidePacketSelfTraffic(t *testing.T) {
+	v4 := netip.MustParseAddr("100.100.1.42")
+	v6 := netip.MustParseAddr("fd00::42")
+
+	tests := []struct {
+		name string
+		addr netip.Addr
+		pkt  []byte
+	}{
+		{"ipv4/tcp", v4, buildIPv4(v4, v4, tcpSyn)},
+		{"ipv4/udp", v4, buildIPv4(v4, v4, udpDatagram)},
+		{"ipv4/icmp", v4, buildIPv4(v4, v4, icmpEcho)},
+		{"ipv6/tcp", v6, buildIPv6(v6, v6, tcpSyn)},
+		{"ipv6/udp", v6, buildIPv6(v6, v6, udpDatagram)},
+		{"ipv6/icmpv6", v6, buildIPv6(v6, v6, icmpv6Echo)},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			f, tun := newSelfForwardInterface(tt.addr)
+			// consumeInsidePacket writes through the slice it is handed, so a
+			// packet that arrived with a valid checksum must come back out of
+			// bytes taken before the call, unchanged.
+			want := append([]byte(nil), tt.pkt...)
+			consumeInside(f, tt.pkt)
+
+			if immediatelyForwardToSelf {
+				require.Len(t, tun.writes, 1)
+				assert.Equal(t, want, tun.writes[0])
+			} else {
+				assert.Empty(t, tun.writes, "self traffic reaches the tun over loopback here and must be dropped")
+			}
+		})
+	}
+}
+
+// TestConsumeInsidePacketSelfTrafficChecksum shows that the self-forward
+// returns the bytes it was handed, so a packet that arrived with a wrong
+// upper-layer checksum is written back with that same wrong checksum and the
+// kernel drops it on re-entry.
+//
+// This is how a macOS host loses TCP and UDP to its own IPv6 overlay address:
+// the kernel writes only the pseudo-header sum into the checksum field and
+// defers completion to hardware offload, state that does not survive the
+// crossing into userspace. Which kernels do this, for which protocols and IP
+// versions, is a property of the kernel and belongs to a test against a live
+// one; here the checksum is simply wrong, and the forward must make it right.
+func TestConsumeInsidePacketSelfTrafficChecksum(t *testing.T) {
+	if !immediatelyForwardToSelf {
+		t.Skip("self traffic never reaches the tun on this platform")
+	}
+	versions := []struct {
+		name  string
+		addr  netip.Addr
+		build func(src, dst netip.Addr, p l4Proto) []byte
+		l4At  int
+		valid func(pkt []byte) bool
+	}{
+		{"v4", netip.MustParseAddr("100.100.1.42"), buildIPv4, ipv4HeaderLen, l4ChecksumValid4},
+		{"v6", netip.MustParseAddr("fd00::42"), buildIPv6, ipv6HeaderLen, l4ChecksumValid6},
+	}
+	for _, v := range versions {
+		for _, p := range []l4Proto{tcpSyn, udpDatagram} {
+			t.Run(v.name+"/"+p.name, func(t *testing.T) {
+				pkt := v.build(v.addr, v.addr, p)
+				binary.BigEndian.PutUint16(pkt[v.l4At+p.cksumAt:], 0x1234)
+				require.False(t, v.valid(pkt), "the packet under test must start with a wrong checksum")
+				f, tun := newSelfForwardInterface(v.addr)
+				consumeInside(f, pkt)
+				require.Len(t, tun.writes, 1)
+				assert.True(t, v.valid(tun.writes[0]),
+					"a forwarded %s packet must carry a valid checksum, got 0x%04x",
+					p.name, binary.BigEndian.Uint16(tun.writes[0][v.l4At+p.cksumAt:]))
+			})
+		}
+	}
+}

interface.go

@@ -2,11 +2,12 @@ package nebula
 
 import (
 	"context"
+	"crypto/fips140"
 	"errors"
 	"fmt"
-	"io"
 	"log/slog"
 	"net/netip"
+	"runtime"
 	"slices"
 	"sync"
 	"sync/atomic"
@@ -14,12 +15,15 @@ import (
 
 	"github.com/gaissmai/bart"
 	"github.com/rcrowley/go-metrics"
+	"github.com/slackhq/nebula/util"
 
 	"github.com/slackhq/nebula/cert"
 	"github.com/slackhq/nebula/config"
 	"github.com/slackhq/nebula/firewall"
 	"github.com/slackhq/nebula/header"
 	"github.com/slackhq/nebula/overlay"
+	"github.com/slackhq/nebula/overlay/batch"
+	"github.com/slackhq/nebula/overlay/tio"
 	"github.com/slackhq/nebula/udp"
 )
 
@@ -39,17 +43,41 @@ type InterfaceConfig struct {
 	DropLocalBroadcast bool
 	DropMulticast      bool
 	routines           int
-	MessageMetrics     *MessageMetrics
-	version            string
-	relayManager       *relayManager
-	punchy             *Punchy
+	// Multiport means the sockets are spread over a range of ports
+	// (listen.port+slot) rather than all sharing listen.port, and that lane
+	// tunnels are negotiated with capable peers.
+	Multiport bool
+	// RoutinesPerPort is how many sockets share each port under multiport, and so
+	// the stride between port slots in writers: writers[s*RoutinesPerPort+r] is
+	// the r'th socket bound to listen.port+s. It is `routines` as configured,
+	// while routines above is that times the number of ports.
+	RoutinesPerPort int
+	// LaneCount is the number of lanes counting the base tunnel as lane 0
+	// (multiport.lanes, clamped to the number of ports bound).
+	LaneCount      int
+	MessageMetrics *MessageMetrics
+	version        string
+	relayManager   *relayManager
+	punchy         *Punchy
 
 	tryPromoteEvery uint32
 	reQueryEvery    uint32
 	reQueryWait     time.Duration
 
 	ConntrackCacheTimeout time.Duration
-	l                     *slog.Logger
+
+	// CpuAffinity, when non-empty, names the CPUs each TUN reader goroutine
+	// should pin to. Queue i pins to CpuAffinity[i % len(CpuAffinity)] —
+	// shorter lists than `routines` cycle. Empty list keeps the default
+	// pin-to-(i % NumCPU) behavior. Only consulted when PinThreads is true.
+	CpuAffinity []int
+	// PinThreads controls whether each TUN reader OS thread is pinned to a
+	// single CPU (via tun.pin_threads, default true). Pinning keeps each
+	// goroutine's sendmmsg on one XPS-selected NIC TX ring so per-flow
+	// packets stay ordered on the wire.
+	PinThreads bool
+
+	l *slog.Logger
 }
 
 type Interface struct {
@@ -71,9 +99,21 @@ type Interface struct {
 	dropLocalBroadcast    bool
 	dropMulticast         bool
 	routines              int
+	multiport             bool
+	routinesPerPort       int
+	laneCount             int
 	disconnectInvalid     atomic.Bool
 	closed                atomic.Bool
-	relayManager          *relayManager
+	// cpuAffinity, when non-empty, names the CPUs each TUN reader goroutine
+	// should pin to. Queue i pins to cpuAffinity[i % len(cpuAffinity)].
+	// Empty falls back to the default pin-to-(allowed CPU) behavior.
+	// Only consulted when pinThreads is true.
+	cpuAffinity []int
+	// pinThreads controls whether listenIn pins each TUN reader OS thread to
+	// a CPU at all (tun.pin_threads, default true). When false, threads are
+	// left free to migrate as on stock nebula.
+	pinThreads   bool
+	relayManager *relayManager
 
 	tryPromoteEvery atomic.Uint32
 	reQueryEvery    atomic.Uint32
@@ -82,16 +122,22 @@ type Interface struct {
 	sendRecvErrorConfig   recvErrorConfig
 	acceptRecvErrorConfig recvErrorConfig
 
-	// rebindCount is used to decide if an active tunnel should trigger a punch notification through a lighthouse
-	rebindCount int8
+	// Bumped on every udp rebind, tunnels compare it to decide they need a punch from the far side
+	rebindEpoch atomic.Uint32
 	version     string
 
 	conntrackCacheTimeout time.Duration
 
 	ctx     context.Context
 	writers []udp.Conn
-	readers []io.ReadWriteCloser
-	wg      sync.WaitGroup
+	queues  []tio.Queue
+	// batchers is one per tun queue, wrapping queues[i]. readOutsidePackets
+	// commits plaintext into the batcher; the plaintext is decrypted
+	// in place inside the UDP receive buffers, so listenOut must call Flush
+	// at the end of each UDP recvmmsg batch, before those buffers are
+	// reused (every udp.Conn ListenOut guarantees that ordering).
+	batchers []*batch.MultiCoalescer
+	wg       sync.WaitGroup
 
 	// fatalErr holds the first unexpected reader error that caused shutdown.
 	// nil means "no fatal error" (yet)
@@ -102,18 +148,13 @@ type Interface struct {
 	metricHandshakes    metrics.Histogram
 	messageMetrics      *MessageMetrics
 	cachedPacketMetrics *cachedPacketMetrics
+	metricTxDropped     metrics.Counter
 
 	l *slog.Logger
 }
 
 type EncWriter interface {
-	SendVia(via *HostInfo,
-		relay *Relay,
-		ad,
-		nb,
-		out []byte,
-		nocopy bool,
-	)
+	SendVia(via *HostInfo, relay *Relay, ad, nb, out []byte, nocopy bool, q int)
 	SendMessageToVpnAddr(t header.MessageType, st header.MessageSubType, vpnAddr netip.Addr, p, nb, out []byte)
 	SendMessageToHostInfo(t header.MessageType, st header.MessageSubType, hostinfo *HostInfo, p, nb, out []byte)
 	Handshake(vpnAddr netip.Addr)
@@ -172,6 +213,10 @@ func NewInterface(ctx context.Context, c *InterfaceConfig) (*Interface, error) {
 		return nil, errors.New("no connection manager")
 	}
 
+	if c.routines <= 1 {
+		c.PinThreads = false //pinning is not useful unless there's more than one tun reader
+	}
+
 	cs := c.pki.getCertState()
 	ifce := &Interface{
 		ctx:                   ctx,
@@ -187,9 +232,12 @@ func NewInterface(ctx context.Context, c *InterfaceConfig) (*Interface, error) {
 		dropLocalBroadcast:    c.DropLocalBroadcast,
 		dropMulticast:         c.DropMulticast,
 		routines:              c.routines,
+		multiport:             c.Multiport,
+		routinesPerPort:       max(c.RoutinesPerPort, 1),
+		laneCount:             c.LaneCount,
 		version:               c.version,
 		writers:               make([]udp.Conn, c.routines),
-		readers:               make([]io.ReadWriteCloser, c.routines),
+		batchers:              make([]*batch.MultiCoalescer, c.routines),
 		myVpnNetworks:         cs.myVpnNetworks,
 		myVpnNetworksTable:    cs.myVpnNetworksTable,
 		myVpnAddrs:            cs.myVpnAddrs,
@@ -198,8 +246,11 @@ func NewInterface(ctx context.Context, c *InterfaceConfig) (*Interface, error) {
 		relayManager:          c.relayManager,
 		connectionManager:     c.connectionManager,
 		conntrackCacheTimeout: c.ConntrackCacheTimeout,
+		cpuAffinity:           c.CpuAffinity,
+		pinThreads:            c.PinThreads,
 
 		metricHandshakes: metrics.GetOrRegisterHistogram("handshakes", nil, metrics.NewExpDecaySample(1028, 0.015)),
+		metricTxDropped:  metrics.GetOrRegisterCounter("udp.tx.dropped", nil),
 		messageMetrics:   c.MessageMetrics,
 		cachedPacketMetrics: &cachedPacketMetrics{
 			sent:    metrics.GetOrRegisterCounter("hostinfo.cached_packets.sent", nil),
@@ -215,6 +266,9 @@ func NewInterface(ctx context.Context, c *InterfaceConfig) (*Interface, error) {
 
 	ifce.connectionManager.intf = ifce
 
+	// Held until Close so waiting on the interface blocks until the resources are actually released
+	ifce.wg.Add(1)
+
 	return ifce, nil
 }
 
@@ -235,40 +289,61 @@ func (f *Interface) activate() error {
 		"build", f.version,
 		"udpAddr", addr,
 		"boringcrypto", boringEnabled(),
+		"fips140Version", fips140.Version(),
+		"fips140Enabled", fips140.Enabled(),
+		"fips140Enforced", fips140.Enforced(),
 	)
 
-	if f.routines > 1 {
-		if !f.inside.SupportsMultiqueue() || !f.outside.SupportsMultipleReaders() {
-			f.routines = 1
-			f.l.Warn("routines is not supported on this platform, falling back to a single routine")
-		}
+	// Under multiport each socket has exactly one reader on its own port, so
+	// the shared-port multi-reader capability is irrelevant (and main.go
+	// already hard-errored on unsupported platforms).
+	if f.routines > 1 && !f.multiport && !f.outside.SupportsMultipleReaders() {
+		f.routines = 1
+		f.l.Warn("multiple udp readers are not supported on this platform, falling back to a single routine")
 	}
 
+	// Prepare the tun queues. A device that can't open that many hands back
+	// fewer (a single queue on platforms without multiqueue support) and we
+	// size the reader routines to what we actually got.
+	queues, err := f.inside.Queues(f.routines)
+	if err != nil {
+		return err
+	}
+	if len(queues) < f.routines {
+		if f.multiport {
+			// The lane sockets are already bound one-per-routine; shrinking
+			// the routine count would leave bound ports with no reader.
+			return fmt.Errorf("multiport requires %d tun queues, device provided %d", f.routines, len(queues))
+		}
+		// TODO: this clamp is only safe because it is unreachable when the
+		// udp side has multiple readers (linux Queues opens exactly n or
+		// errors; every other platform already clamped routines to 1 above).
+		// If a platform ever returns fewer queues than routines with
+		// SO_REUSEPORT sockets already bound, the surplus sockets get no
+		// listenOut and the kernel blackholes every flow it hashes to them —
+		// fail loudly or close the extra sockets instead.
+		f.l.Warn("tun multiqueue is not supported on this platform, falling back to fewer routines",
+			"requested", f.routines, "opened", len(queues))
+		f.routines = len(queues)
+	}
+	f.queues = queues
+
 	metrics.GetOrRegisterGauge("routines", nil).Update(int64(f.routines))
 
-	// Prepare n tun queues
-	var reader io.ReadWriteCloser = f.inside
-	for i := 0; i < f.routines; i++ {
-		if i > 0 {
-			reader, err = f.inside.NewMultiQueueReader()
-			if err != nil {
-				return err
-			}
-		}
-		f.readers[i] = reader
+	for i := range f.queues {
+		f.batchers[i] = batch.NewMultiCoalescer(f.queues[i], f.l)
 	}
 
-	f.wg.Add(1) // for us to wait on Close() to return
+	// On error the caller owns the cleanup, Control.Start cancels the service context
+	// before releasing our resources so a waiter never observes a live context
 	if err = f.inside.Activate(); err != nil {
-		f.wg.Done()
-		f.inside.Close()
 		return err
 	}
 
 	return nil
 }
 
-func (f *Interface) run() (func() error, error) {
+func (f *Interface) run() {
 	// Launch n queues to read packets from udp
 	for i := 0; i < f.routines; i++ {
 		f.wg.Go(func() {
@@ -279,17 +354,18 @@ func (f *Interface) run() (func() error, error) {
 	// Launch n queues to read packets from tun dev
 	for i := 0; i < f.routines; i++ {
 		f.wg.Go(func() {
-			f.listenIn(f.readers[i], i)
+			f.listenIn(f.queues[i], i)
 		})
 	}
 
-	return func() error {
-		f.wg.Wait()
-		if e := f.fatalErr.Load(); e != nil {
-			return *e
-		}
-		return nil
-	}, nil
+}
+
+func (f *Interface) wait() error {
+	f.wg.Wait()
+	if e := f.fatalErr.Load(); e != nil {
+		return *e
+	}
+	return nil
 }
 
 // onFatal stores the first fatal reader error, and calls triggerShutdown if it was the first one
@@ -303,6 +379,31 @@ func (f *Interface) onFatal(err error) {
 	}
 }
 
+type rxContext struct {
+	q       int
+	scratch []byte
+	// nb is a re-usable nonce buffer for decrypt calls to use
+	nb           []byte
+	h            *header.H
+	fwPacket     *firewall.ParsedPacket
+	hostmapCache map[uint32]*HostInfo
+	lhh          *LightHouseHandler
+	ctCache      *firewall.ConntrackCacheTicker
+}
+
+func newRxContext(f *Interface, q int) *rxContext {
+	return &rxContext{
+		q:            q,
+		scratch:      make([]byte, mtu),
+		nb:           make([]byte, 12, 12),
+		h:            &header.H{},
+		fwPacket:     &firewall.ParsedPacket{},
+		hostmapCache: map[uint32]*HostInfo{},
+		lhh:          f.lightHouse.NewRequestHandler(),
+		ctCache:      firewall.NewConntrackCacheTicker(f.ctx, f.l, f.conntrackCacheTimeout),
+	}
+}
+
 func (f *Interface) listenOut(i int) {
 	var li udp.Conn
 	if i > 0 {
@@ -311,18 +412,25 @@ func (f *Interface) listenOut(i int) {
 		li = f.outside
 	}
 
-	ctCache := firewall.NewConntrackCacheTicker(f.ctx, f.l, f.conntrackCacheTimeout)
-	lhh := f.lightHouse.NewRequestHandler()
-	plaintext := make([]byte, udp.MTU)
-	h := &header.H{}
-	fwPacket := &firewall.Packet{}
-	nb := make([]byte, 12, 12)
+	rxc := newRxContext(f, i)
 
-	err := li.ListenOut(func(fromUdpAddr netip.AddrPort, payload []byte) {
-		f.readOutsidePackets(ViaSender{UdpAddr: fromUdpAddr}, plaintext[:0], payload, h, fwPacket, lhh, nb, i, ctCache.Get())
-	})
+	listener := func(fromUdpAddr netip.AddrPort, payload []byte) {
+		f.readOutsidePackets(ViaSender{UdpAddr: fromUdpAddr, SockIdx: i}, payload, rxc)
+	}
 
-	if err != nil && !f.closed.Load() {
+	flusher := func() {
+		if err := f.batchers[i].Flush(); err != nil {
+			f.l.Error("Failed to flush tun coalescer", "error", err)
+		}
+		clear(rxc.hostmapCache)
+	}
+
+	err := li.ListenOut(listener, flusher)
+
+	// An error after teardown began is shutdown noise, the closed flag covers resources
+	// Close releases itself and the cancelled ctx covers ones torn down by their owners
+	// reacting to it, like the user device pipes
+	if err != nil && !f.closed.Load() && f.ctx.Err() == nil {
 		f.l.Error("Error while reading inbound packet, closing", "error", err)
 		f.onFatal(err)
 	}
@@ -330,30 +438,187 @@ func (f *Interface) listenOut(i int) {
 	f.l.Debug("underlay reader is done", "reader", i)
 }
 
-func (f *Interface) listenIn(reader io.ReadWriteCloser, i int) {
-	packet := make([]byte, mtu)
-	out := make([]byte, mtu)
-	fwPacket := &firewall.Packet{}
+func (f *Interface) pinThisThread(i int) {
+	var cpu int
+	if n := len(f.cpuAffinity); n > 0 {
+		// Explicit tun.cpu_affinity list wins; parseCpuAffinity already
+		// validated the entries against the allowed CPU set.
+		cpu = f.cpuAffinity[i%n]
+	} else if allowed, err := util.AllowedCPUs(); err == nil && len(allowed) > 0 {
+		// Default: spread queues across the CPUs we're actually allowed to
+		// run on. Under a cpuset/taskset mask these aren't 0..NumCPU-1, so
+		// i % NumCPU would pick unrunnable IDs and every pin would fail.
+		cpu = allowed[i%len(allowed)]
+	} else {
+		cpu = i % runtime.NumCPU()
+	}
+	if err := util.PinThreadToCPU(cpu); err != nil {
+		f.l.Warn("failed to pin tun reader to CPU", "queue", i, "cpu", cpu, "err", err)
+	}
+}
+
+// txQueue is the per-routine TX state owned by one listenIn goroutine.
+//
+// base carries base-session data, relay carriers, and everything on a tunnel
+// without lanes. It goes out a socket on the base port — egressSock's pick — since
+// base traffic must keep the base source port or a vanilla peer would see it move
+// and roam-thrash. lane[s] goes out a socket on listen.port+s and carries traffic
+// encrypted with lane s's session; lane[0] is base, and the rest are built on the
+// first packet that picks them, since a routine that never sends on a lane should
+// not hold a batch for it. Both come from laneSock, so a routine writes to its own
+// share of each port's socket group.
+//
+// Which lane a packet rides comes from its own flow hash, not from this
+// routine's index. That is deliberate. Which routine reads a flow is the
+// kernel's decision: it hashes the flow to a tun queue, but it also *learns*
+// the queue we write that flow's inbound packets to, and prefers what it
+// learned. So if the lane followed the routine, a peer whose lanes were still
+// down — every peer, for the first moments of a tunnel — would write all of its
+// inbound traffic to queue 0, teaching both kernels to steer every flow to
+// queue 0, and every tunnel would collapse onto lane 0 and stay there for as
+// long as its flows kept busy. Hashing here makes lane spread independent of
+// tun steering entirely.
+//
+// Every batch borrows arena, so a routine holding a batch per lane still costs
+// one slab. The arena is reset by flush once every batch over it is drained.
+//
+// Several routines can still write to one socket — the sockets on a port are
+// shared by the routines whose lane arithmetic lands on them — which the underlay
+// serializes (see batchWriter). Per-flow wire order still holds: a flow is hashed
+// onto one lane and read by one routine, so nothing else is writing it.
+type txQueue struct {
+	// q is the queue this state belongs to, which laneSock needs to resolve a lane
+	// to one of its port's sockets.
+	q     int
+	base  *batch.SendBatch
+	lane  []*batch.SendBatch
+	arena *batch.Arena
+
+	// live is every batch built so far, in build order, so base is first: see
+	// flush. Kept as its own slice because lane is mostly nil holes and both
+	// full and flush walk this per read batch.
+	live []txBatch
+}
+
+// txBatch is a live batch and the index in writers of the socket it flushes to.
+type txBatch struct {
+	sb   *batch.SendBatch
+	sock int
+}
+
+func (f *Interface) newTxQueue(q int) *txQueue {
+	baseSock := f.egressSock(q)
+	arena := batch.NewArena(batch.SendBatchCap * (udp.MTU + 32))
+	base := batch.NewSendBatchSharedArena(f.writers[baseSock], batch.SendBatchCap, arena)
+
+	tx := &txQueue{
+		q:     q,
+		base:  base,
+		arena: arena,
+		live:  []txBatch{{sb: base, sock: baseSock}},
+	}
+	if f.multiport && f.laneCount > 1 {
+		tx.lane = make([]*batch.SendBatch, f.laneCount)
+		tx.lane[0] = base
+	}
+	return tx
+}
+
+// laneBatch returns the batch for lane s, building it the first time this
+// routine sends on that lane. Lanes this queue doesn't cover fall back to base,
+// which is also lane 0's batch.
+func (tx *txQueue) laneBatch(f *Interface, s int) *batch.SendBatch {
+	if s <= 0 || s >= len(tx.lane) {
+		return tx.base
+	}
+	sb := tx.lane[s]
+	if sb == nil {
+		sock := f.laneSock(tx.q, s)
+		sb = batch.NewSendBatchSharedArena(f.writers[sock], batch.SendBatchCap, tx.arena)
+		tx.lane[s] = sb
+		tx.live = append(tx.live, txBatch{sb: sb, sock: sock})
+	}
+	return sb
+}
+
+// full reports a full sendmmsg worth of work queued across every lane, rather
+// than on any one of them: the arena is shared, so it is the total that bounds
+// how much is outstanding.
+func (tx *txQueue) full() bool {
+	n := 0
+	for _, b := range tx.live {
+		n += b.sb.Len()
+	}
+	return n >= batch.SendBatchCap
+}
+
+// flush drains base before the lanes so that when a flow moves from the base
+// session onto a freshly promoted lane mid-window, its packets still leave this
+// host in encryption order. Resetting the shared arena is this queue's job,
+// since no single batch's Flush can know the others are done with it.
+func (tx *txQueue) flush(f *Interface) {
+	for _, b := range tx.live {
+		if b.sb.Len() > 0 {
+			f.flushSendBatch(b.sb, b.sock)
+		}
+	}
+	tx.arena.Reset()
+}
+
+func (f *Interface) listenIn(queue tio.Queue, i int) {
+	// Pinning this thread (and goroutine) to a single CPU keeps every sendmmsg from this goroutine going through the
+	// same TX ring on the nic, so the wire sees per-flow order. Skip entirely when tun.pin_threads is false.
+	if f.pinThreads {
+		f.pinThisThread(i)
+	}
+
+	rejectBuf := make([]byte, mtu)
+	tx := f.newTxQueue(i)
+	fwPacket := &firewall.ParsedPacket{}
 	nb := make([]byte, 12, 12)
 
 	conntrackCache := firewall.NewConntrackCacheTicker(f.ctx, f.l, f.conntrackCacheTimeout)
 
 	for {
-		n, err := reader.Read(packet)
+		pkts, err := queue.Read()
 		if err != nil {
-			if !f.closed.Load() {
+			// Same shutdown noise handling as listenOut
+			if !f.closed.Load() && f.ctx.Err() == nil {
 				f.l.Error("Error while reading outbound packet, closing", "error", err, "reader", i)
 				f.onFatal(err)
 			}
 			break
 		}
 
-		f.consumeInsidePacket(packet[:n], fwPacket, nb, out, i, conntrackCache.Get())
+		for _, pkt := range pkts {
+			f.consumeInsidePacket(pkt, fwPacket, nb, tx, rejectBuf, i, conntrackCache.Get())
+			// Flush incrementally once a full sendmmsg batch has
+			// accumulated so the first packets of a deep read drain
+			// hit the wire while the rest are still being encrypted.
+			if tx.full() {
+				tx.flush(f)
+			}
+		}
+		tx.flush(f)
 	}
 
 	f.l.Debug("overlay reader is done", "reader", i)
 }
 
+// flushSendBatch drains sb to the underlay and accounts for anything it could not deliver. A shortfall means
+// specific destinations were undeliverable (a stale remote, a reject rule), which the backend logs per peer at
+// debug; here it is only a counter, so one unreachable peer cannot spam a log line per batch.
+func (f *Interface) flushSendBatch(sb *batch.SendBatch, q int) {
+	queued := sb.Len()
+	written, err := sb.Flush()
+	if err != nil {
+		f.l.Error("Failed to write outgoing batch", "error", err, "writer", q)
+	}
+	if dropped := queued - written; dropped > 0 {
+		f.metricTxDropped.Inc(int64(dropped))
+	}
+}
+
 func (f *Interface) RegisterConfigChangeCallbacks(c *config.C) {
 	c.RegisterReloadCallback(f.reloadFirewall)
 	c.RegisterReloadCallback(f.reloadSendRecvError)
@@ -502,11 +767,23 @@ func (f *Interface) emitStats(ctx context.Context, i time.Duration) {
 	certInitiatingVersion := metrics.GetOrRegisterGauge("certificate.initiating_version", nil)
 	certMaxVersion := metrics.GetOrRegisterGauge("certificate.max_version", nil)
 
+	// Registered only when we run multiport, so these don't sit at zero on a node
+	// that was never going to have a lane and read as a broken feature.
+	var lanesUpGauge, laneTunnelsGauge metrics.Gauge
+	if f.multiport && f.laneCount > 1 {
+		lanesUpGauge = metrics.GetOrRegisterGauge("multiport.lanes.up", nil)
+		laneTunnelsGauge = metrics.GetOrRegisterGauge("multiport.lanes.tunnels", nil)
+	}
+
 	emit := func() {
 		f.firewall.EmitStats()
 		f.handshakeManager.EmitStats()
 		udpStats()
 
+		if lanesUpGauge != nil {
+			f.emitLaneStats(lanesUpGauge, laneTunnelsGauge)
+		}
+
 		certState := f.pki.getCertState()
 		defaultCrt := certState.GetDefaultCertificate()
 		certExpirationGauge.Update(int64(defaultCrt.NotAfter().Sub(time.Now()) / time.Second))
@@ -542,9 +819,15 @@ func (f *Interface) GetCertState() *CertState {
 	return f.pki.getCertState()
 }
 
+// Close releases the interface's resources: the udp sockets and the tun device.
+// It is idempotent and safe to call at any point in the lifecycle, including on an interface that never activated,
+// calls after the first return nil without doing anything.
 func (f *Interface) Close() error {
+	if !f.closed.CompareAndSwap(false, true) {
+		return nil
+	}
+
 	var errs []error
-	f.closed.Store(true)
 
 	// Release the udp readers
 	for i, u := range f.writers {
@@ -560,6 +843,8 @@ func (f *Interface) Close() error {
 	if closeErr != nil {
 		errs = append(errs, closeErr)
 	}
+
+	// Release the construction token so waiters know the resources are gone
 	f.wg.Done()
 	return errors.Join(errs...)
 }

iputil/checksum.go

@@ -0,0 +1,146 @@
+package iputil
+
+import (
+	"encoding/binary"
+
+	"github.com/slackhq/nebula/overlay/checksum"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+const udpHeaderLen = 8
+
+// SetTransportChecksum recomputes the TCP or UDP checksum of an IPv4 or IPv6
+// packet in place.
+//
+// A kernel that offloads checksums to the NIC hands a packet to a tun with the
+// transport checksum unfinished: only the pseudo-header sum is in the field and
+// the rest is left for hardware that a tun does not have. A packet written
+// straight back to that tun is dropped on re-entry unless the checksum is
+// completed first. ICMP is left alone; it arrived complete on the kernels this
+// was measured against.
+//
+// So is any packet whose transport header cannot be located: fragments, unknown
+// extension headers and truncated packets. An IPv6 fragment header is declined
+// even when it carries the whole datagram (RFC 6946 atomic fragment), because
+// the walk reports only that a fragment header was present.
+func SetTransportChecksum(packet []byte) {
+	if len(packet) < 1 {
+		return
+	}
+	switch int(packet[0] >> 4) {
+	case ipv4.Version:
+		setTransportChecksum4(packet)
+	case ipv6.Version:
+		setTransportChecksum6(packet)
+	}
+}
+
+func setTransportChecksum4(packet []byte) {
+	if len(packet) < ipv4.HeaderLen {
+		return
+	}
+	ihl := int(packet[0]&0x0f) << 2
+	end := int(binary.BigEndian.Uint16(packet[2:4]))
+	if ihl < ipv4.HeaderLen || end < ihl || end > len(packet) {
+		return
+	}
+	// The checksum covers the whole datagram, which a fragment (MF set or a
+	// non-zero offset) does not carry.
+	if binary.BigEndian.Uint16(packet[6:8])&0x3fff != 0 {
+		return
+	}
+
+	transport, ok := transportExtent(packet[ihl:end], packet[9])
+	if !ok {
+		return
+	}
+	csum := ipv4PseudoheaderChecksum(packet[12:16], packet[16:20], uint32(packet[9]), uint32(len(transport)))
+	writeTransportChecksum(transport, packet[9], csum)
+}
+
+func setTransportChecksum6(packet []byte) {
+	if len(packet) < ipv6.HeaderLen {
+		return
+	}
+	end := ipv6.HeaderLen + int(binary.BigEndian.Uint16(packet[4:6]))
+	if end > len(packet) {
+		return
+	}
+
+	// The checksum covers the whole datagram, which a fragment does not carry.
+	// An unknown extension header hides where the transport header starts. A
+	// chain longer than the walk's budget ends it early, at an offset that was
+	// never checked against the packet.
+	proto, offset, _, anyFragment, err := IPv6FindUpperProtocol(packet[:end])
+	if err != nil || anyFragment || offset >= end {
+		return
+	}
+
+	transport, ok := transportExtent(packet[offset:end], proto)
+	if !ok {
+		return
+	}
+	csum := ipv6PseudoheaderChecksum(packet[8:24], packet[24:40], uint32(proto), uint32(len(transport)))
+	writeTransportChecksum(transport, proto, csum)
+}
+
+// transportExtent narrows a segment to the length its own header declares. UDP
+// carries a Length field, and RFC 768 and RFC 8200 section 8.1 both make that
+// field, not the IP payload extent, the length the pseudo-header counts and the
+// checksum covers; a datagram padded out to a link's minimum frame is the usual
+// way the two differ. TCP has no such field, so its segment runs to the end of
+// the IP payload. A Length that overruns the bytes IP delivered describes a
+// datagram that is not there.
+func transportExtent(transport []byte, proto uint8) ([]byte, bool) {
+	if proto != IPProtocolUDP {
+		return transport, true
+	}
+	if len(transport) < udpHeaderLen {
+		return nil, false
+	}
+	ulen := int(binary.BigEndian.Uint16(transport[4:6]))
+	if ulen < udpHeaderLen || ulen > len(transport) {
+		return nil, false
+	}
+	return transport[:ulen], true
+}
+
+// writeTransportChecksum stores the checksum of transport, taken over the
+// pseudo-header sum csum, in the header's checksum field. A UDP checksum that
+// computes to zero goes on the wire as 0xffff: zero means no checksum was
+// computed (RFC 768), and over IPv6 the checksum is mandatory (RFC 8200
+// section 8.1).
+func writeTransportChecksum(transport []byte, proto uint8, csum uint32) {
+	var at, minLen int
+	switch proto {
+	case IPProtocolTCP:
+		at, minLen = 16, 20
+	case IPProtocolUDP:
+		at, minLen = 6, udpHeaderLen
+	default:
+		return
+	}
+	if len(transport) < minLen {
+		return
+	}
+
+	transport[at], transport[at+1] = 0, 0
+	sum := ^checksum.Checksum(transport, fold(csum))
+	if sum == 0 && proto == IPProtocolUDP {
+		sum = 0xffff
+	}
+	binary.BigEndian.PutUint16(transport[at:], sum)
+}
+
+// fold reduces a pseudo-header sum to the 16 bit seed Checksum takes. Carrying
+// the high half back into the low half is what keeps the reduction lossless, so
+// the seed sums exactly as the wider value would; 0xffff is its fixed point.
+// Every term of that sum comes from a 16 bit field, so it stays far below the
+// width at which the accumulator would wrap.
+func fold(csum uint32) uint16 {
+	for csum > 0xffff {
+		csum = (csum >> 16) + (csum & 0xffff)
+	}
+	return uint16(csum)
+}

iputil/checksum_test.go

@@ -0,0 +1,242 @@
+package iputil
+
+import (
+	"encoding/binary"
+	"net"
+	"testing"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/ipv6"
+)
+
+// serialize builds a packet with gopacket, whose checksums are computed
+// independently of this package.
+func serialize(t *testing.T, ls ...gopacket.SerializableLayer) []byte {
+	buf := gopacket.NewSerializeBuffer()
+	require.NoError(t, gopacket.SerializeLayers(buf, gopacket.SerializeOptions{FixLengths: true, ComputeChecksums: true}, ls...))
+	return append([]byte(nil), buf.Bytes()...)
+}
+
+// withExtensionHeader inserts an 8 byte IPv6 extension header of the given
+// type between the IPv6 header and its payload. The transport checksum does not
+// change: the pseudo-header counts only upper-layer bytes.
+func withExtensionHeader(pkt []byte, typ layers.IPProtocol, hdr [8]byte) []byte {
+	hdr[0] = pkt[6]
+	out := make([]byte, 0, len(pkt)+8)
+	out = append(out, pkt[:40]...)
+	out = append(out, hdr[:]...)
+	out = append(out, pkt[40:]...)
+	out[6] = byte(typ)
+	binary.BigEndian.PutUint16(out[4:6], binary.BigEndian.Uint16(pkt[4:6])+8)
+	return out
+}
+
+// truncate copies the first n bytes into a buffer of exactly that capacity, so
+// a read past the length panics instead of quietly succeeding.
+func truncate(pkt []byte, n int) []byte {
+	out := make([]byte, n)
+	copy(out, pkt)
+	return out
+}
+
+// extChain builds an IPv6 packet fronted by n Destination Options headers. Each
+// points at another one, so the walk spends its whole budget without reaching a
+// transport header. lastExtLen inflates the final header's declared length,
+// which is how the walk ends up past the end of the packet.
+func extChain(n int, lastExtLen byte) []byte {
+	pkt := make([]byte, ipv6.HeaderLen)
+	pkt[0], pkt[6], pkt[7] = 0x60, 60, 64
+	for i := range n {
+		h := make([]byte, 8)
+		h[0] = 60
+		if i == n-1 {
+			h[1] = lastExtLen
+		}
+		pkt = append(pkt, h...)
+	}
+	pkt = append(pkt, make([]byte, 20)...)
+	binary.BigEndian.PutUint16(pkt[4:6], uint16(len(pkt)-ipv6.HeaderLen))
+	return pkt
+}
+
+func TestSetTransportChecksum(t *testing.T) {
+	// Source and destination differ so that a pseudo-header built from the wrong
+	// one, or from the two swapped, does not land on the same checksum anyway.
+	v4 := func(proto layers.IPProtocol) *layers.IPv4 {
+		return &layers.IPv4{Version: 4, TTL: 64, Id: 0x1234, Protocol: proto, SrcIP: net.IPv4(192, 0, 2, 1).To4(), DstIP: net.IPv4(198, 51, 100, 2).To4()}
+	}
+	v6 := func(proto layers.IPProtocol) *layers.IPv6 {
+		return &layers.IPv6{Version: 6, HopLimit: 64, NextHeader: proto, SrcIP: net.ParseIP("2001:db8::1"), DstIP: net.ParseIP("2001:db8:1::2")}
+	}
+	tcp := func(ip gopacket.NetworkLayer) *layers.TCP {
+		l := &layers.TCP{SrcPort: 49152, DstPort: 443, SYN: true, Window: 65535}
+		require.NoError(t, l.SetNetworkLayerForChecksum(ip))
+		return l
+	}
+	udp := func(ip gopacket.NetworkLayer) *layers.UDP {
+		l := &layers.UDP{SrcPort: 49152, DstPort: 53}
+		require.NoError(t, l.SetNetworkLayerForChecksum(ip))
+		return l
+	}
+	payload := gopacket.Payload("self")
+	nop := layers.IPv4Option{OptionType: 1, OptionLength: 1}
+
+	ip4tcp := v4(layers.IPProtocolTCP)
+	ip4opts := v4(layers.IPProtocolTCP)
+	ip4opts.Options = []layers.IPv4Option{nop, nop, nop, nop}
+	ip4udp := v4(layers.IPProtocolUDP)
+	ip6tcp := v6(layers.IPProtocolTCP)
+	ip6udp := v6(layers.IPProtocolUDP)
+	hopByHop := [8]byte{0, 0, 1, 4} // next header, length 0, PadN of 4
+
+	// Bytes past the length the IP header declares are not part of the
+	// datagram and must not be summed.
+	trailing4 := append(serialize(t, ip4tcp, tcp(ip4tcp), payload), []byte("trailing")...)
+	trailing6 := append(serialize(t, ip6tcp, tcp(ip6tcp), payload), []byte("trailing")...)
+
+	// A datagram padded out past the length UDP declares: the pseudo-header
+	// counts the UDP Length field, so the checksum is the unpadded one.
+	padded4 := append(serialize(t, ip4udp, udp(ip4udp), payload), []byte("pad!")...)
+	binary.BigEndian.PutUint16(padded4[2:4], uint16(len(padded4)))
+	padded6 := append(serialize(t, ip6udp, udp(ip6udp), payload), []byte("pad!")...)
+	binary.BigEndian.PutUint16(padded6[4:6], uint16(len(padded6)-ipv6.HeaderLen))
+
+	// Corrupting the checksum and asking for it back must yield gopacket's
+	// packet, byte for byte.
+	recomputed := []struct {
+		name  string
+		pkt   []byte
+		cksum int
+	}{
+		{"v4 tcp", serialize(t, ip4tcp, tcp(ip4tcp), payload), 20 + 16},
+		{"v4 tcp with ip options", serialize(t, ip4opts, tcp(ip4opts), payload), 24 + 16},
+		{"v4 udp", serialize(t, ip4udp, udp(ip4udp), payload), 20 + 6},
+		{"v4 tcp header only", serialize(t, ip4tcp, tcp(ip4tcp)), 20 + 16},
+		{"v4 udp header only", serialize(t, ip4udp, udp(ip4udp)), 20 + 6},
+		{"v6 tcp", serialize(t, ip6tcp, tcp(ip6tcp), payload), 40 + 16},
+		{"v6 udp", serialize(t, ip6udp, udp(ip6udp), payload), 40 + 6},
+		{"v6 udp header only", serialize(t, ip6udp, udp(ip6udp)), 40 + 6},
+		{"v6 tcp behind hop-by-hop", withExtensionHeader(serialize(t, ip6tcp, tcp(ip6tcp), payload), layers.IPProtocolIPv6HopByHop, hopByHop), 48 + 16},
+		{"v4 tcp with bytes past the total length", trailing4, 20 + 16},
+		{"v6 tcp with bytes past the payload length", trailing6, 40 + 16},
+		{"v4 udp padded past its declared length", padded4, 20 + 6},
+		{"v6 udp padded past its declared length", padded6, 40 + 6},
+	}
+	for _, tt := range recomputed {
+		t.Run(tt.name, func(t *testing.T) {
+			got := append([]byte(nil), tt.pkt...)
+			binary.BigEndian.PutUint16(got[tt.cksum:], 0x1234)
+			require.NotEqual(t, tt.pkt, got)
+			SetTransportChecksum(got)
+			assert.Equal(t, tt.pkt, got)
+		})
+	}
+
+	ip4frag := v4(layers.IPProtocolTCP)
+	ip4frag.Flags = layers.IPv4MoreFragments
+	ip4later := v4(layers.IPProtocolTCP)
+	ip4later.FragOffset = 1
+	ip4icmp := v4(layers.IPProtocolICMPv4)
+
+	badIHL := serialize(t, ip4tcp, tcp(ip4tcp), payload)
+	badIHL[0] = 0x44 // header length 16, shorter than an ipv4 header
+	shortTotalLen := serialize(t, ip4tcp, tcp(ip4tcp), payload)
+	binary.BigEndian.PutUint16(shortTotalLen[2:4], 10) // shorter than the header it introduces
+	cutTCP := serialize(t, ip4tcp, tcp(ip4tcp), payload)
+	binary.BigEndian.PutUint16(cutTCP[2:4], 20+19) // one byte short of a tcp header
+	cutTCP = truncate(cutTCP, 20+19)
+	cutUDP := serialize(t, ip4udp, udp(ip4udp), payload)
+	binary.BigEndian.PutUint16(cutUDP[2:4], 20+7) // one byte short of a udp header
+	cutUDP = truncate(cutUDP, 20+7)
+	// Two bytes short, so a transport header survives whole and the minimum
+	// length check cannot stand in for the bounds check.
+	cutV6 := truncate(serialize(t, ip6tcp, tcp(ip6tcp), payload), 62)
+	fragment := [8]byte{0, 0, 0, 1, 0, 0, 0, 1} // next header, reserved, offset 0 with M set, id
+	overrun4 := serialize(t, ip4udp, udp(ip4udp), payload)
+	binary.BigEndian.PutUint16(overrun4[24:26], uint16(len(overrun4)-20+1)) // one byte past what ip delivered
+	overrun6 := serialize(t, ip6udp, udp(ip6udp), payload)
+	binary.BigEndian.PutUint16(overrun6[44:46], uint16(len(overrun6)-ipv6.HeaderLen+1))
+	shortUDPLen := serialize(t, ip4udp, udp(ip4udp), payload)
+	binary.BigEndian.PutUint16(shortUDPLen[24:26], 7) // shorter than the header it counts
+
+	// Where the checksum cannot be completed the packet is left as it came.
+	untouched := []struct {
+		name  string
+		pkt   []byte
+		cksum int
+	}{
+		{"v4 first fragment", serialize(t, ip4frag, tcp(ip4frag), payload), 20 + 16},
+		{"v4 later fragment", serialize(t, ip4later, tcp(ip4later), payload), 20 + 16},
+		{"v4 icmp", serialize(t, ip4icmp, &layers.ICMPv4{TypeCode: layers.CreateICMPv4TypeCode(8, 0), Id: 1, Seq: 1}, payload), 20 + 2},
+		{"v4 header length below the minimum", badIHL, 20 + 16},
+		{"v4 total length below the header length", shortTotalLen, 20 + 16},
+		{"v4 truncated below its total length", truncate(serialize(t, ip4tcp, tcp(ip4tcp), payload), 30), -1},
+		{"v4 tcp header cut short", cutTCP, 20 + 16},
+		{"v4 udp header cut short", cutUDP, -1},
+		{"v6 fragment", withExtensionHeader(serialize(t, ip6tcp, tcp(ip6tcp), payload), layers.IPProtocolIPv6Fragment, fragment), 48 + 16},
+		{"v6 truncated below its payload length", truncate(serialize(t, ip6tcp, tcp(ip6tcp), payload), 50), -1},
+		{"v6 truncated with a whole transport header still present", cutV6, 40 + 16},
+		{"v6 extension header chain longer than the walk", extChain(9, 0), 112 + 16},
+		{"v6 extension header chain running past the packet", extChain(8, 255), 104 + 16},
+		{"v4 udp length past the end of the datagram", overrun4, 20 + 6},
+		{"v6 udp length past the end of the datagram", overrun6, 40 + 6},
+		{"v4 udp length below a udp header", shortUDPLen, 20 + 6},
+	}
+	for _, tt := range untouched {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.cksum >= 0 {
+				binary.BigEndian.PutUint16(tt.pkt[tt.cksum:], 0x1234)
+			}
+			want := append([]byte(nil), tt.pkt...)
+			SetTransportChecksum(tt.pkt)
+			assert.Equal(t, want, tt.pkt)
+		})
+	}
+
+	t.Run("too short to carry a header", func(t *testing.T) {
+		for _, pkt := range [][]byte{nil, {}, {0x45}, {0x60}} {
+			assert.NotPanics(t, func() { SetTransportChecksum(pkt) })
+		}
+	})
+
+	t.Run("tcp checksum of zero goes out as zero", func(t *testing.T) {
+		pkt := serialize(t, ip4tcp, tcp(ip4tcp), gopacket.Payload{0, 0})
+		c := binary.BigEndian.Uint16(pkt[36:38])
+		require.NotZero(t, c)
+		// Only udp reserves zero to mean "not computed", so tcp keeps it.
+		binary.BigEndian.PutUint16(pkt[40:42], c)
+		SetTransportChecksum(pkt)
+		assert.Zero(t, binary.BigEndian.Uint16(pkt[36:38]))
+	})
+
+	t.Run("udp checksum of zero goes out as 0xffff", func(t *testing.T) {
+		pkt := serialize(t, ip4udp, udp(ip4udp), gopacket.Payload{0, 0})
+		c := binary.BigEndian.Uint16(pkt[26:28])
+		require.NotZero(t, c)
+		// The one's complement sum is now 0xffff - c; adding c to the payload
+		// makes it 0xffff, whose complement is zero.
+		binary.BigEndian.PutUint16(pkt[28:30], c)
+		SetTransportChecksum(pkt)
+		assert.Equal(t, uint16(0xffff), binary.BigEndian.Uint16(pkt[26:28]))
+	})
+}
+
+func TestFold(t *testing.T) {
+	// 0xffff is the fold's fixed point, so a loop bound one notch tight never
+	// terminates on it.
+	for _, tt := range []struct {
+		in   uint32
+		want uint16
+	}{
+		{0, 0},
+		{0xffff, 0xffff},
+		{0x10000, 1},
+		{0x1fffe, 0xffff},
+		{0xffffffff, 0xffff},
+	} {
+		assert.Equal(t, tt.want, fold(tt.in))
+	}
+}

iputil/packet.go

@@ -2,11 +2,16 @@ package iputil
 
 import (
 	"encoding/binary"
+	"errors"
 
 	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
 )
 
+// ErrIPv6CouldNotFindPayload is returned when the ipv6 extension header chain is truncated before a terminal
+// upper layer protocol is reached.
+var ErrIPv6CouldNotFindPayload = errors.New("could not find payload in ipv6 packet")
+
 const (
 	// MaxIPv4RejectPacketSize is the largest IPv4 reject packet:
 	// - 20 byte ipv4 header
@@ -22,6 +27,13 @@ const (
 	maxIPv6RejectPacketSize = ipv6.HeaderLen + 8 + 1000
 
 	MaxRejectPacketSize = maxIPv6RejectPacketSize
+
+	IPProtocolICMP        = 1
+	IPProtocolICMPv6      = 58
+	IPProtocolTCP         = 6
+	IPProtocolUDP         = 17
+	ICMPv6TypeEchoRequest = 128
+	ICMPv6TypeEchoReply   = 129
 )
 
 func CreateRejectPacket(packet []byte, out []byte) []byte {
@@ -199,8 +211,8 @@ func ipv4CreateRejectTCPPacket(packet []byte, out []byte) []byte {
 }
 
 func ipv6CreateRejectPacket(packet []byte, out []byte) []byte {
-	proto, offset, isFragment := ipv6FindUpperProtocol(packet)
-	if isFragment {
+	proto, offset, isFragment, _, err := IPv6FindUpperProtocol(packet)
+	if err != nil || isFragment {
 		return nil
 	}
 	switch proto {
@@ -333,40 +345,60 @@ func ipv6CreateRejectTCPPacket(packet []byte, out []byte, offset int) []byte {
 	return out
 }
 
-func ipv6FindUpperProtocol(packet []byte) (nextHeader uint8, offset int, isFragment bool) {
+// IPv6FindUpperProtocol walks the ipv6 extension header chain and returns the upper layer protocol, the
+// offset it begins at, and whether the packet is a non-first fragment. Only the RFC 8200 and IANA extension
+// headers below are walked. Everything else, including Mobility (135), HIP (139), Shim6 (140), experimental
+// 253/254, and real upper layer protocols like SCTP or GRE, is terminal. Walking those as extension headers
+// is a firewall bypass, so they fail closed. For a non-first fragment the returned protocol is the fragmented
+// protocol and offset points at the fragment header, there is no transport header to locate. Returns
+// ErrIPv6CouldNotFindPayload if packet is smaller than an ipv6 header or the chain is truncated before a
+// terminal protocol is reached.
+func IPv6FindUpperProtocol(packet []byte) (nextHeader uint8, offset int, isFragment bool, anyFragment bool, err error) {
+	const maxIPv6ExtHeaders = 8
+	if len(packet) < ipv6.HeaderLen {
+		return 0, 0, false, false, ErrIPv6CouldNotFindPayload
+	}
 	nextHeader = packet[6]
 	offset = ipv6.HeaderLen
 
-	for {
+	for range maxIPv6ExtHeaders {
 		switch nextHeader {
 		case 0, 43, 60: // Hop-by-Hop, Routing, Destination
 			if len(packet) < offset+2 {
-				return nextHeader, offset, isFragment
+				return nextHeader, offset, isFragment, anyFragment, ErrIPv6CouldNotFindPayload
 			}
 			nextHeader = packet[offset]
 			offset += (int(packet[offset+1]) + 1) << 3
 
 		case 44: // Fragment
 			if len(packet) < offset+8 {
-				return nextHeader, offset, isFragment
+				return nextHeader, offset, isFragment, anyFragment, ErrIPv6CouldNotFindPayload
 			}
+			anyFragment = true
+			// Non-first fragments carry no transport header, report the fragmented protocol and stop
 			if packet[offset+2] != 0 || packet[offset+3]&0xf8 != 0 {
-				isFragment = true
+				return packet[offset], offset, true, anyFragment, nil
 			}
 			nextHeader = packet[offset]
 			offset += 8
 
 		case 51: // AH
 			if len(packet) < offset+2 {
-				return nextHeader, offset, isFragment
+				return nextHeader, offset, isFragment, anyFragment, ErrIPv6CouldNotFindPayload
 			}
 			nextHeader = packet[offset]
 			offset += (int(packet[offset+1]) + 2) << 2
 
 		default:
-			return nextHeader, offset, isFragment
+			// A prior extension header can declare a length that advances offset past the packet. The terminal
+			// protocol's header isn't actually here, so treat the chain as truncated rather than classifying it.
+			if offset > len(packet) {
+				return nextHeader, offset, isFragment, anyFragment, ErrIPv6CouldNotFindPayload
+			}
+			return nextHeader, offset, isFragment, anyFragment, nil
 		}
 	}
+	return nextHeader, offset, isFragment, anyFragment, nil
 }
 
 func CreateICMPEchoResponse(packet, out []byte) []byte {

iputil/packet_test.go

@@ -1,11 +1,13 @@
 package iputil
 
 import (
+	"bytes"
 	"encoding/binary"
 	"net"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
 )
@@ -179,6 +181,46 @@ func Test_CreateRejectPacket_NoICMPError(t *testing.T) {
 	}
 }
 
+// Test_CreateRejectPacket_RespectsCap ensures it is impossible for
+// an oversized ICMPv6 reject to overwrite the neighbor segment's bytes.
+func Test_CreateRejectPacket_RespectsCap(t *testing.T) {
+	src := net.ParseIP("fd00::1")
+	dst := net.ParseIP("fd00::2")
+
+	// Inner IPv6 UDP packet. An ICMPv6 reject copies the whole inner packet
+	// plus a 48-byte header (40 IPv6 + 8 ICMPv6), so it needs 48 more bytes
+	// than the inner packet length.
+	inner := makeIPv6Packet(src, dst, 17, make([]byte, 20))
+
+	// The ciphertext scratch reused as the reject buffer is the received
+	// datagram: 16-byte Nebula header + inner + 16-byte AEAD tag. That is only
+	// 32 bytes of slack, so a full ICMPv6 reject overruns it by 16 bytes.
+	const nebulaOverhead = 32
+	segLen := len(inner) + nebulaOverhead
+
+	// Shared backing row laid out as [segment][neighbor's 16-byte Nebula header].
+	const neighborHdr = 16
+	sentinel := bytes.Repeat([]byte{0xAB}, neighborHdr)
+
+	// Uncapped: the slice's capacity reaches into the neighbor, reproducing
+	// the overrun that silently drops the neighbor packet.
+	backing := make([]byte, segLen+neighborHdr)
+	copy(backing[segLen:], sentinel)
+	reject := CreateRejectPacket(inner, backing[:segLen])
+	assert.NotNil(t, reject, "uncapped buffer reaches into the neighbor, so the reject is built")
+	assert.NotEqual(t, sentinel, backing[segLen:segLen+neighborHdr],
+		"without the cap the oversized reject overruns into the neighbor segment")
+
+	// Capped (the fix): cap==len, so the builder cannot exceed the segment. The
+	// reject does not fit, so it is refused rather than corrupting the neighbor.
+	backing = make([]byte, segLen+neighborHdr)
+	copy(backing[segLen:], sentinel)
+	reject = CreateRejectPacket(inner, backing[:segLen:segLen])
+	assert.Nil(t, reject, "capped segment is 16 bytes too small for a full ICMPv6 reject, so it is refused")
+	assert.Equal(t, sentinel, backing[segLen:segLen+neighborHdr],
+		"capped segment must leave the neighbor untouched")
+}
+
 func makeIPv6Packet(src, dst net.IP, nextHeader uint8, payload []byte) []byte {
 	b := make([]byte, ipv6.HeaderLen+len(payload))
 	b[0] = ipv6.Version << 4
@@ -474,3 +516,63 @@ func TestCreateICMPEchoResponse_IPv6_NotICMPv6(t *testing.T) {
 	result := CreateICMPEchoResponse(packet, out)
 	assert.Nil(t, result)
 }
+
+func Test_IPv6FindUpperProtocol(t *testing.T) {
+	src := net.ParseIP("fd00::1")
+	dst := net.ParseIP("fd00::2")
+
+	// 8 byte extension/transport stand-ins, first byte is the next header, second is the length field
+	extToTCP := []byte{6, 0, 0, 0, 0, 0, 0, 0}        // len 0 -> 8 bytes, next = TCP
+	extToUDP := []byte{17, 0, 0, 0, 0, 0, 0, 0}       // len 0 -> 8 bytes, next = UDP
+	extToRouting := []byte{43, 0, 0, 0, 0, 0, 0, 0}   // len 0 -> 8 bytes, next = Routing
+	ahToUDP := []byte{17, 0, 0, 0, 0, 0, 0, 0}        // AH len 0 -> (0+2)<<2 = 8 bytes, next = UDP
+	firstFragToUDP := []byte{17, 0, 0, 1, 0, 0, 0, 1} // frag offset 0, M=1, next = UDP
+	nonFirstFrag := []byte{17, 0, 0, 9, 0, 0, 0, 1}   // frag offset non-zero, next = UDP
+	transport := []byte{0, 80, 1, 187, 0, 0, 0, 0}    // stand-in bytes, IPv6FindUpperProtocol never reads ports
+
+	tests := []struct {
+		name         string
+		nextHeader   uint8
+		payload      []byte
+		wantProto    uint8
+		wantOffset   int
+		wantFragment bool
+		wantAnyFrag  bool
+		wantErr      error
+	}{
+		{"plain udp", 17, transport, 17, ipv6.HeaderLen, false, false, nil},
+		{"hop-by-hop then tcp", 0, append(extToTCP, transport...), 6, ipv6.HeaderLen + 8, false, false, nil},
+		{"routing then tcp", 43, append(extToTCP, transport...), 6, ipv6.HeaderLen + 8, false, false, nil},
+		{"destination then udp", 60, append(extToUDP, transport...), 17, ipv6.HeaderLen + 8, false, false, nil},
+		{"hop-by-hop, routing, then tcp", 0, append(append(extToRouting, extToTCP...), transport...), 6, ipv6.HeaderLen + 16, false, false, nil},
+		{"ah then udp", 51, append(ahToUDP, transport...), 17, ipv6.HeaderLen + 8, false, false, nil},
+		{"first fragment walks to transport", 44, append(firstFragToUDP, transport...), 17, ipv6.HeaderLen + 8, false, true, nil},
+		{"non-first fragment stops", 44, append(nonFirstFrag, transport...), 17, ipv6.HeaderLen, true, true, nil},
+		{"unknown protocol is terminal", 132, transport, 132, ipv6.HeaderLen, false, false, nil}, // SCTP
+		{"truncated extension header", 0, nil, 0, ipv6.HeaderLen, false, false, ErrIPv6CouldNotFindPayload},
+		// Destination Options with a declared length (255+1)*8 = 2048 that runs past the 48 byte buffer, next = SCTP
+		{"extension length past buffer", 60, []byte{132, 255, 0, 0, 0, 0, 0, 0}, 132, ipv6.HeaderLen + 2048, false, false, ErrIPv6CouldNotFindPayload},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			packet := makeIPv6Packet(src, dst, tt.nextHeader, tt.payload)
+			proto, offset, isFragment, anyFragment, err := IPv6FindUpperProtocol(packet)
+			if tt.wantErr != nil {
+				assert.ErrorIs(t, err, tt.wantErr)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tt.wantProto, proto)
+			assert.Equal(t, tt.wantOffset, offset)
+			assert.Equal(t, tt.wantFragment, isFragment)
+			assert.Equal(t, tt.wantAnyFrag, anyFragment)
+		})
+	}
+
+	// A packet smaller than an ipv6 header must error rather than panic reading byte 6
+	t.Run("shorter than ipv6 header", func(t *testing.T) {
+		_, _, _, _, err := IPv6FindUpperProtocol(make([]byte, 6))
+		assert.ErrorIs(t, err, ErrIPv6CouldNotFindPayload)
+	})
+}

lanes.go

@@ -0,0 +1,713 @@
+package nebula
+
+import (
+	"context"
+	"hash/fnv"
+	"log/slog"
+	"net/netip"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/flynn/noise"
+	"github.com/rcrowley/go-metrics"
+	"github.com/slackhq/nebula/cert"
+	"github.com/slackhq/nebula/firewall"
+	"github.com/slackhq/nebula/handshake"
+	"github.com/slackhq/nebula/header"
+	"github.com/slackhq/nebula/noiseutil"
+)
+
+// Multiport lanes give one tunnel several underlay 5-tuples, so its traffic
+// spreads over ECMP paths, NIC receive queues and per-flow policers instead of
+// funnelling through a single flow. Each inside flow picks a lane by hashing its
+// own 5-tuple, so the spread doesn't depend on how a kernel steers tun queues
+// (see txQueue).
+//
+// A lane is not a second tunnel: it is an extra session on the same HostInfo.
+// Noise leaves us with A.eKey == B.dKey, so both sides expand the same two keys
+// with the same per-lane label and land on a matched pair without exchanging
+// anything. A lane therefore costs no handshake, has no half-established state,
+// and dies exactly when its base tunnel does. Which lane a packet belongs to
+// travels in the nebula header, inside the AEAD's associated data.
+//
+// Lane 0 is the base tunnel itself: HostInfo.ConnectionState, the base port, and
+// the peer's real remote address, and it carries its share of flows like any
+// other. Lane s > 0 egresses a socket on listen.port+s (see laneSock) toward the
+// peer's advertised port range. Receiving on a lane
+// needs no permission — the keys are derivable the moment the base handshake
+// completes — but sending on one needs proof the new 5-tuple actually works,
+// since nothing else would notice a middlebox quietly dropping it. So a lane
+// stays down until a probe on it is acked, and falls back to the base tunnel the
+// moment it stops being acked.
+//
+// Both directions are pay-per-use. A lane session is derived on the first packet
+// that needs it, because how many lanes exist is partly the peer's call: it
+// advertises how many it sends on, and we have to be able to receive all of
+// them. Deriving them all up front would let a peer advertising the maximum cost
+// us a replay window and two cipher states per lane, per tunnel, for lanes it
+// may never send on.
+
+const (
+	// laneKeyInfo is the HKDF label prefix for lane key expansion. Changing it
+	// means older builds derive different keys and drop our lane traffic; the
+	// base tunnel would keep working, so the failure would be a silent loss of
+	// lanes rather than of connectivity.
+	laneKeyInfo = "nebula multiport lane v1"
+
+	// laneRetryBase and laneRetryMax bound the backoff between probes of a lane
+	// that will not come up, so a peer whose lane ports are firewalled costs one
+	// packet a minute rather than one per traffic tick.
+	laneRetryBase = 5 * time.Second
+	laneRetryMax  = 60 * time.Second
+
+	// laneMaxFails caps the failure counter; the backoff saturates well before.
+	laneMaxFails = 8
+
+	// laneProbeTimeout is how long a probe may go unacked before it counts as a
+	// failure. It is shorter than the connection manager's check interval on
+	// purpose: an outstanding probe is judged on the next tick either way, and a
+	// longer timeout would only delay that by a whole tick.
+	laneProbeTimeout = 2 * time.Second
+
+	// laneKeepalive is how often a lane that is up re-proves its path. Traffic
+	// on a lane is not evidence the lane works — that is the whole reason lanes
+	// need probing — so a lane that silently breaks is only caught here.
+	laneKeepalive = 30 * time.Second
+)
+
+// laneSet holds a peer's lane sessions and the state deciding which lanes may
+// carry traffic. It is built when the base handshake completes and never
+// resized, so the slices and their lengths are immutable; mu guards the fields
+// under it, and sessions/txAddr/demand are atomics read by the data plane
+// without it.
+type laneSet struct {
+	// sessions[s] holds lane s's session once something has needed it, and nil
+	// until then. sessions[0] is never populated: lane 0 is the base tunnel's own
+	// ConnectionState. The length is immutable, so the data plane bounds-checks
+	// and loads with no locking.
+	sessions []atomic.Pointer[ConnectionState]
+
+	// material is what a lane session is derived from, kept because sessions are
+	// derived lazily and the handshake result is long gone by then.
+	material laneMaterial
+
+	// txAddr[s] holds lane s's remote address while the lane is proven usable
+	// and nil otherwise. This single atomic is both the TX gate and the
+	// destination, so a routine that loads non-nil has everything it needs.
+	// Sized txLanes: lanes above that never send.
+	txAddr []atomic.Pointer[netip.AddrPort]
+
+	// demand[s] is raised at creation, and again by the TX path whenever a flow
+	// hashes onto lane s while it is down. Probing is demand-driven, so a peer we
+	// never send to costs nothing beyond its base tunnel no matter how many lanes
+	// are configured, and a lane that keeps failing is only retried while
+	// something still wants it. Sized txLanes.
+	demand []atomic.Bool
+
+	// txLanes is how many lanes we may send on — our lane count clamped to the
+	// ports the peer bound — and so the modulus a flow's hash is reduced by.
+	// Lanes from txLanes up can only receive, which is how a peer with more
+	// routines than us still spreads its own traffic.
+	// Immutable, and the length of every TX-side slice here.
+	txLanes int
+
+	mu sync.Mutex
+
+	// peerPortCount and peerBasePort are the peer's advertised port range and
+	// portOffset is this pair's rotation within it: lane s targets
+	// peerBasePort + ((s + portOffset) % peerPortCount).
+	peerPortCount uint16
+	peerBasePort  uint16
+	portOffset    uint16
+
+	// laneBias rotates the flow hash before it picks a lane, so the two sides of
+	// a flow land on lanes that are each other's partner rather than at
+	// independent points in the range. See newLaneSet.
+	laneBias uint16
+
+	// peerAddr is the address the current lane targets were built from. The
+	// peer's lane ports have no derivable relationship to a new NAT mapping, so
+	// a roam invalidates every lane rather than moving it.
+	peerAddr netip.Addr
+
+	// probe[s] is lane s's probe and backoff state. Sized txLanes.
+	probe []laneProbeState
+}
+
+// laneMaterial is everything a lane session is derived from. The two base keys
+// are the same secret the base tunnel's own cipher states already hold — the
+// noiseutil.CipherState interface just doesn't hand them back, so a lane set
+// keeps its own copy rather than a reference to the session.
+type laneMaterial struct {
+	eKey, dKey [32]byte
+	cipher     noise.CipherFunc
+	myCert     cert.Certificate
+	peerCert   *cert.CachedCertificate
+	initiator  bool
+}
+
+type laneProbeState struct {
+	// gen is the generation of the last probe sent, echoed in the ack so a late
+	// ack cannot promote a lane on the strength of a superseded probe.
+	gen uint8
+
+	// fails is the consecutive failure count driving retryAt.
+	fails uint8
+
+	// sentAt is when the outstanding probe went out, zero when none is pending.
+	sentAt time.Time
+
+	// target is where the outstanding probe went, promoted to txAddr on ack. It
+	// outlives the probe, which is what lets a demotion log the address that
+	// stopped answering.
+	target netip.AddrPort
+
+	// lastAck is when the lane was last confirmed usable, driving the keepalive.
+	lastAck time.Time
+
+	// retryAt is the earliest we may probe this lane again.
+	retryAt time.Time
+}
+
+// newLaneSet sets up the lanes for a freshly completed base handshake. It
+// returns nil when the pair has no lane beyond the base tunnel, which is the
+// normal answer for a peer running without multiport. No session is derived
+// here; each is derived on the first packet that needs it.
+func newLaneSet(r *handshake.Result, myLanes int, myAddr, peerAddr netip.Addr) *laneSet {
+	// PeerPortCount and PeerBasePort are already bounded to uint16 by the
+	// handshake payload parser. A zero port count is a peer that did not
+	// advertise multiport at all, so there is no lane to be had in either
+	// direction.
+	peerPorts := uint16(r.PeerPortCount)
+	if peerPorts == 0 {
+		return nil
+	}
+
+	// Sessions have to cover both directions: we send on our lanes and receive
+	// on the peer's, and one derived session serves both ends of a lane index.
+	// Only the session table is sized by the peer's advertised count; the TX-side
+	// state is sized by what we will actually send on.
+	n := min(max(myLanes, int(r.PeerTxLanes)), header.MaxLane+1)
+	if n < 2 {
+		return nil
+	}
+	txLanes := min(myLanes, int(peerPorts), n)
+
+	offset := lanePortOffset(myAddr, peerAddr, peerPorts)
+
+	// A flow picks its lane from a hash both sides compute identically, so with
+	// the ranges lined up the two directions of a flow would pick the same lane
+	// index — and lane s targets the peer's lane (s + portOffset), not lane s. The
+	// high-addressed side rotates its choice by the low side's offset, which is
+	// its own negated, so the two directions land on partner lanes and their
+	// 4-tuples are exact reverses: each side's traffic then arrives through the
+	// conntrack entry the other's probe opened. With mismatched ranges there are
+	// no partner lanes to find, so don't pretend: hash straight.
+	bias := uint16(0)
+	if txLanes == int(peerPorts) && peerAddr.Less(myAddr) {
+		bias = (peerPorts - offset) % peerPorts
+	}
+
+	ls := &laneSet{
+		sessions: make([]atomic.Pointer[ConnectionState], n),
+		material: laneMaterial{
+			eKey:      r.EKey.UnsafeKey(),
+			dKey:      r.DKey.UnsafeKey(),
+			cipher:    r.Cipher,
+			myCert:    r.MyCert,
+			peerCert:  r.RemoteCert,
+			initiator: r.Initiator,
+		},
+		txAddr:        make([]atomic.Pointer[netip.AddrPort], txLanes),
+		demand:        make([]atomic.Bool, txLanes),
+		probe:         make([]laneProbeState, txLanes),
+		txLanes:       txLanes,
+		peerPortCount: peerPorts,
+		peerBasePort:  uint16(r.PeerBasePort),
+		portOffset:    offset,
+		laneBias:      bias,
+	}
+
+	// Every lane starts out demanded, so the first traffic tick on this tunnel
+	// probes all of them at once instead of waiting for a flow to hash onto each.
+	// Lanes have to be up *before* the flows are, not after: the peer writes a
+	// flow's inbound packets to the tun queue matching the socket they arrived on,
+	// and the kernel remembers that for as long as the flow stays busy. A flow that
+	// starts while the lanes are still down therefore gets pinned to queue 0 on
+	// both hosts for its whole life. This costs one probe per lane on any tunnel
+	// with traffic; an idle tunnel is never ticked, so it still costs nothing.
+	for s := 1; s < txLanes; s++ {
+		ls.demand[s].Store(true)
+	}
+	return ls
+}
+
+// laneLogAttr summarizes what a tunnel negotiated, for the handshake log lines.
+// It is an empty attr, which slog drops, on a node not running multiport. A peer
+// that negotiated no lanes still logs, with zeros: "we offered and got nothing"
+// is exactly what you want to see when you expected lanes and have none.
+func laneLogAttr(myLanes int, ls *laneSet) slog.Attr {
+	if myLanes == 0 {
+		return slog.Attr{}
+	}
+	if ls == nil {
+		return slog.Any("lanes", m{"tx": 0, "sessions": 0})
+	}
+	// Every field read here is immutable once the set is built.
+	return slog.Any("lanes", m{
+		"tx":           ls.txLanes,
+		"sessions":     len(ls.sessions),
+		"peerBasePort": ls.peerBasePort,
+		"peerPorts":    ls.peerPortCount,
+		"portOffset":   ls.portOffset,
+	})
+}
+
+// emitLaneStats reports how many lanes are carrying traffic and how many tunnels
+// have any. Both are counted by walking the hostmap, because a counter kept at
+// promotion and demotion would drift upward forever: a tunnel torn down while its
+// lanes are up never demotes them. Only a node running multiport pays for the
+// walk.
+func (f *Interface) emitLaneStats(up, tunnels metrics.Gauge) {
+	var nUp, nTunnels int64
+	f.hostMap.ForEachIndex(func(hostinfo *HostInfo) {
+		ls := hostinfo.lanes
+		if ls == nil {
+			return
+		}
+		nTunnels++
+		for s := 1; s < ls.txLanes; s++ {
+			if ls.txAddr[s].Load() != nil {
+				nUp++
+			}
+		}
+	})
+	up.Update(nUp)
+	tunnels.Update(nTunnels)
+}
+
+// lanePortOffset returns the rotation applied to this pair's lane target ports,
+// in [0, peerPortCount). Without it every low-routine peer would aim its few
+// lanes at a big peer's first few ports, concentrating the big peer's receive
+// work on a couple of sockets; the hash spreads pairs across the whole range.
+//
+// Both sides hash the same sorted vpn-address pair and the higher address
+// negates the result, so when port counts match the two sides' rotations
+// cancel: our lane s's 4-tuple stays the reverse of the peer's lane s, and each
+// side's probe opens the conntrack entry the other's arrives through. (The one
+// lane a nonzero rotation lands on the peer's base port has no partner lane, so
+// behind a port-restricted NAT it is the one lane that may never come up.)
+func lanePortOffset(myAddr, peerAddr netip.Addr, peerPortCount uint16) uint16 {
+	if peerPortCount == 0 {
+		return 0
+	}
+	lo, hi := myAddr, peerAddr
+	if hi.Less(lo) {
+		lo, hi = hi, lo
+	}
+	h := fnv.New32a()
+	b := lo.As16()
+	h.Write(b[:])
+	b = hi.As16()
+	h.Write(b[:])
+	o := uint16(h.Sum32() % uint32(peerPortCount))
+	if myAddr == hi {
+		o = (peerPortCount - o) % peerPortCount
+	}
+	return o
+}
+
+// laneSession returns the session to decrypt a lane s packet with, deriving one
+// if this is the first packet to claim that lane. A nil session with no error
+// means this tunnel has no lane s at all.
+//
+// cached reports whether the session was already in the table. A fresh one is
+// deliberately left out of it: anyone who can spoof this tunnel's local index
+// can name any lane, and installing on sight would let them make us hold a
+// replay window and two cipher states per lane without authenticating anything.
+// The caller must install with installSession once the packet decrypts, which is
+// the first moment the lane is known to be real.
+func (i *HostInfo) laneSession(s uint8) (ci *ConnectionState, cached bool, err error) {
+	ls := i.lanes
+	if ls == nil || s == 0 || int(s) >= len(ls.sessions) {
+		return nil, false, nil
+	}
+
+	if cs := ls.sessions[s].Load(); cs != nil {
+		return cs, true, nil
+	}
+
+	cs, err := newLaneConnectionState(&ls.material, s)
+	if err != nil {
+		return nil, false, err
+	}
+	return cs, false, nil
+}
+
+// installSession publishes a session derived by laneSession, so the next packet
+// on the lane doesn't have to derive it again. cs must have already decrypted the
+// packet at messageCounter.
+//
+// Two routines can race on a lane's first packet and derive a session each. The
+// loser's is dropped, and with it the replay-window entry for the packet it just
+// accepted, so hand that counter to the session that survives — the keys are
+// identical, so it is the same window in every respect that matters.
+func (ls *laneSet) installSession(l *slog.Logger, s uint8, cs *ConnectionState, messageCounter uint64) {
+	if ls.sessions[s].CompareAndSwap(nil, cs) {
+		return
+	}
+	ls.sessions[s].Load().noteSeen(l, messageCounter)
+}
+
+// session returns lane s's session for our own use, deriving and installing it
+// if it doesn't exist yet. Unlike the RX path this needs no proof the lane is
+// real: we only ask for lanes we chose to send on. s must be a lane this set
+// covers.
+func (ls *laneSet) session(s int) (*ConnectionState, error) {
+	if cs := ls.sessions[s].Load(); cs != nil {
+		return cs, nil
+	}
+
+	cs, err := newLaneConnectionState(&ls.material, uint8(s))
+	if err != nil {
+		return nil, err
+	}
+
+	if !ls.sessions[s].CompareAndSwap(nil, cs) {
+		return ls.sessions[s].Load(), nil
+	}
+	return cs, nil
+}
+
+// maxMessageCounter returns the highest counter across the base session and
+// every lane session. Data rides the lanes, so the base counter alone would
+// never reach the rehandshake or exhaustion thresholds and the lane keys would
+// be used past their data-volume margin. Rolling the base tunnel replaces the
+// lane keys with it, since lanes are derived from it.
+func (i *HostInfo) maxMessageCounter() uint64 {
+	if i.ConnectionState == nil {
+		return 0
+	}
+	c := i.ConnectionState.messageCounter.Load()
+	if ls := i.lanes; ls != nil {
+		for s := range ls.sessions {
+			cs := ls.sessions[s].Load()
+			if cs == nil {
+				// Never derived, so it has never sent anything either.
+				continue
+			}
+			if lc := cs.messageCounter.Load(); lc > c {
+				c = lc
+			}
+		}
+	}
+	return c
+}
+
+// txLane returns the session and destination for lane s, or a nil session when
+// the lane is down and the caller must use the base tunnel. A miss raises
+// demand, which is what gets a down lane probed again, so we pay for a lane
+// exactly where real traffic wanted one. Callers on the data plane come through
+// txLaneForFlow.
+func (ls *laneSet) txLane(s int) (*ConnectionState, netip.AddrPort) {
+	if ls == nil || s <= 0 || s >= ls.txLanes {
+		return nil, netip.AddrPort{}
+	}
+
+	if addr := ls.txAddr[s].Load(); addr != nil {
+		// The lane is only up because a probe was acked on it, and that probe
+		// derived the session, so this load cannot miss. Fall back rather than
+		// derive here anyway: this is the hot path and a nil is not worth an HKDF.
+		if cs := ls.sessions[s].Load(); cs != nil {
+			return cs, *addr
+		}
+		return nil, netip.AddrPort{}
+	}
+
+	// Load-guarded so the common case of a lane that will not come up is a
+	// plain read and cannot ping-pong the cache line these flags share.
+	if !ls.demand[s].Load() {
+		ls.demand[s].Store(true)
+	}
+	return nil, netip.AddrPort{}
+}
+
+// txLaneForFlow picks the lane a flow rides and returns it with its session and
+// destination, or lane 0 and a nil session when the flow belongs on the base
+// tunnel — either because the hash landed on lane 0 or because the lane it
+// landed on is down.
+//
+// The lane comes from the flow rather than from the sending routine so that lane
+// use doesn't depend on how the kernel steers tun queues; see txQueue. It is a
+// pure function of the 5-tuple, so a flow stays on one lane for its life: no
+// per-packet reordering, and one lane's replay window sees one set of flows.
+func (ls *laneSet) txLaneForFlow(p *firewall.Packet) (int, *ConnectionState, netip.AddrPort) {
+	if ls == nil || ls.txLanes < 2 {
+		return 0, nil, netip.AddrPort{}
+	}
+
+	s := int((laneFlowHash(p) + uint32(ls.laneBias)) % uint32(ls.txLanes))
+	if s == 0 {
+		// Lane 0 is the base tunnel, and a full share of flows belongs on it.
+		return 0, nil, netip.AddrPort{}
+	}
+
+	cs, addr := ls.txLane(s)
+	return s, cs, addr
+}
+
+// laneFlowHash hashes a 5-tuple to the same value from either end of the flow,
+// which is what lets both peers pick partner lanes for it (see laneBias). FNV-1a
+// by hand rather than through hash/fnv: this runs per packet, and the interface
+// there would escape the addresses to the heap.
+func laneFlowHash(p *firewall.Packet) uint32 {
+	// Order the two endpoints so the direction of travel cannot change the hash.
+	aAddr, aPort := p.LocalAddr, p.LocalPort
+	bAddr, bPort := p.RemoteAddr, p.RemotePort
+	if bAddr.Less(aAddr) || (aAddr == bAddr && bPort < aPort) {
+		aAddr, aPort, bAddr, bPort = bAddr, bPort, aAddr, aPort
+	}
+
+	const prime = 16777619
+	h := uint32(2166136261)
+	x, y := aAddr.As16(), bAddr.As16()
+	for i := range x {
+		h = (h ^ uint32(x[i])) * prime
+		h = (h ^ uint32(y[i])) * prime
+	}
+	for _, b := range [5]byte{byte(aPort >> 8), byte(aPort), byte(bPort >> 8), byte(bPort), p.Protocol} {
+		h = (h ^ uint32(b)) * prime
+	}
+	return h
+}
+
+// laneTargetPortLocked returns the peer port lane s aims at. Only meaningful
+// when peerPortCount is nonzero, which txLanes > 0 guarantees.
+func (ls *laneSet) laneTargetPortLocked(s int) uint16 {
+	return ls.peerBasePort + uint16((s+int(ls.portOffset))%int(ls.peerPortCount))
+}
+
+// laneTargetLocked returns where lane s's probes go: the peer port this lane is
+// paired with, on the peer's current direct address.
+//
+// A lane only ever aims at its own port. There is no fallback to the peer's base
+// port when the lane port doesn't answer — a lane sharing the base port's
+// destination gains only a source port of its own, while costing the peer the
+// receive spread that is the whole point, so a lane that can't reach its port
+// stays down and its traffic rides the base tunnel.
+func (ls *laneSet) laneTargetLocked(s int, addr netip.Addr) netip.AddrPort {
+	return netip.AddrPortFrom(addr, ls.laneTargetPortLocked(s))
+}
+
+// laneRetryDelay is the backoff after fails consecutive probe failures.
+func laneRetryDelay(fails uint8) time.Duration {
+	d := laneRetryBase << min(fails, 4)
+	if d > laneRetryMax {
+		d = laneRetryMax
+	}
+	return d
+}
+
+// noteAck records an acked probe for lane s, promoting the lane if it was down.
+// gen must match the outstanding probe. Reports the target the lane came up on,
+// and whether this ack is what promoted it.
+func (ls *laneSet) noteAck(s int, gen uint8, now time.Time) (netip.AddrPort, bool) {
+	if s <= 0 || s >= len(ls.probe) {
+		return netip.AddrPort{}, false
+	}
+
+	ls.mu.Lock()
+	defer ls.mu.Unlock()
+
+	p := &ls.probe[s]
+	if p.sentAt.IsZero() || p.gen != gen {
+		// No probe outstanding, or an ack for a probe we have already given up
+		// on. Either way it says nothing about the lane's current path.
+		return netip.AddrPort{}, false
+	}
+
+	p.sentAt = time.Time{}
+	p.lastAck = now
+	p.fails = 0
+	p.retryAt = time.Time{}
+
+	target := p.target
+	if ls.txAddr[s].Load() != nil {
+		// Keepalive for a lane already up.
+		return target, false
+	}
+
+	ls.txAddr[s].Store(&target)
+	return target, true
+}
+
+// probeLanes runs one lane maintenance pass for a peer: it demotes lanes whose
+// probe went unanswered, re-proves lanes that have been up a while without one,
+// and probes down lanes the data plane asked for. Driven by the connection
+// manager's per-tunnel traffic tick, which only fires for a live tunnel — the
+// same condition that produces lane demand in the first place.
+func (f *Interface) probeLanes(hostinfo *HostInfo, now time.Time, nb, out []byte) {
+	ls := hostinfo.lanes
+	if ls == nil || ls.txLanes < 2 {
+		return
+	}
+
+	remote := hostinfo.GetRemote()
+
+	ls.mu.Lock()
+	defer ls.mu.Unlock()
+
+	if !remote.IsValid() {
+		// Relayed, or otherwise without a direct path. Lanes are direct-only,
+		// so drop them all; a later tick rebuilds if a direct path returns.
+		ls.resetLocked()
+		return
+	}
+
+	if ls.peerAddr != remote.Addr() {
+		if ls.peerAddr.IsValid() {
+			// A roam is a new path, not a failure: forget the lanes built on
+			// the old one and let demand re-probe from a clean backoff. On the
+			// first pass there is nothing built yet, so just record the address.
+			ls.resetLocked()
+		}
+		ls.peerAddr = remote.Addr()
+	}
+
+	for s := 1; s < ls.txLanes; s++ {
+		p := &ls.probe[s]
+		up := ls.txAddr[s].Load() != nil
+
+		if !p.sentAt.IsZero() {
+			if now.Sub(p.sentAt) < laneProbeTimeout {
+				continue
+			}
+
+			// An aged-out probe is a failure whether it was bringing the lane
+			// up or keeping it up.
+			p.sentAt = time.Time{}
+			p.fails = min(p.fails+1, laneMaxFails)
+			p.retryAt = now.Add(laneRetryDelay(p.fails))
+			if up {
+				ls.txAddr[s].Store(nil)
+				hostinfo.logger(f.l).Info("Multiport lane demoted, probe unanswered", "lane", s, "udpAddr", p.target)
+			}
+			continue
+		}
+
+		if up {
+			if now.Sub(p.lastAck) < laneKeepalive {
+				continue
+			}
+		} else if now.Before(p.retryAt) || !ls.demand[s].Swap(false) {
+			continue
+		}
+
+		p.gen++
+		p.target = ls.laneTargetLocked(s, remote.Addr())
+		if f.sendLaneProbe(hostinfo, s, p.gen, p.target, nb, out) {
+			p.sentAt = now
+		} else {
+			p.fails = min(p.fails+1, laneMaxFails)
+			p.retryAt = now.Add(laneRetryDelay(p.fails))
+		}
+	}
+}
+
+// resetLocked takes every lane down and clears its probe state, without
+// counting it as a failure.
+//
+// Demand is deliberately left standing: it records that a routine has real
+// traffic for this peer, which a roam or a relay detour does not change. Keeping
+// it re-probes the lanes that were actually carrying data as soon as a path
+// exists again, while a lane whose routine has gone quiet stays down.
+func (ls *laneSet) resetLocked() {
+	for s := 1; s < len(ls.probe); s++ {
+		ls.txAddr[s].Store(nil)
+		ls.probe[s] = laneProbeState{}
+	}
+}
+
+// sendLaneProbe sends a probe on lane s to addr from a socket on lane s's port.
+// The probe is an ordinary Test packet encrypted with the lane's session, so an
+// ack proves the whole lane: our source port reached the peer, its reply reached
+// us, and the keys we derived for this lane match the ones it derived. Reports
+// whether the probe made it onto the wire.
+//
+// It goes out the first socket on the port, since the connection manager runs
+// this and has no queue of its own; every socket on the port has the same address,
+// so the probe proves the path for whichever one the data plane picks.
+func (f *Interface) sendLaneProbe(hostinfo *HostInfo, s int, gen uint8, addr netip.AddrPort, nb, out []byte) bool {
+	// The first probe on a lane is what derives its session.
+	ci, err := hostinfo.lanes.session(s)
+	if err != nil {
+		hostinfo.logger(f.l).Error("Failed to derive multiport lane session", "error", err, "lane", s)
+		return false
+	}
+	if ci == nil || ci.eKey == nil {
+		return false
+	}
+
+	if noiseutil.EncryptLockNeeded {
+		ci.writeLock.Lock()
+	}
+	c, ok := ci.NextMessageCounter()
+	if !ok {
+		if noiseutil.EncryptLockNeeded {
+			ci.writeLock.Unlock()
+		}
+		f.dropExhausted(hostinfo, c, "Dropping multiport lane probe, lane message counter is exhausted")
+		return false
+	}
+
+	b := header.EncodeLane(out[:0], header.Version, header.Test, header.LaneProbe, hostinfo.remoteIndexId, c, uint8(s))
+	b, err = ci.eKey.EncryptDanger(b, b, []byte{uint8(s), gen}, c, nb)
+	if noiseutil.EncryptLockNeeded {
+		ci.writeLock.Unlock()
+	}
+	if err != nil {
+		hostinfo.logger(f.l).Error("Failed to encrypt multiport lane probe", "error", err, "lane", s)
+		return false
+	}
+
+	f.messageMetrics.Tx(header.Test, header.LaneProbe, 1)
+	if err := f.writers[f.laneSock(0, s)].WriteTo(b, addr); err != nil {
+		hostinfo.logger(f.l).Error("Failed to send multiport lane probe", "error", err, "lane", s, "udpAddr", addr)
+		return false
+	}
+
+	if f.l.Enabled(context.Background(), slog.LevelDebug) {
+		hostinfo.logger(f.l).Debug("Multiport lane probe sent", "lane", s, "gen", gen, "udpAddr", addr)
+	}
+	return true
+}
+
+// handleLaneProbe answers a peer's lane probe. The ack rides the base tunnel on
+// purpose: a probe proves the peer's lane s works in its send direction, and
+// answering on our own lane s would make the result depend on a second path
+// that may be broken independently.
+func (f *Interface) handleLaneProbe(hostinfo *HostInfo, lane uint8, payload []byte, rxc *rxContext) {
+	if lane == 0 || len(payload) < 2 {
+		return
+	}
+
+	// Echo the header's lane rather than the payload's, so a peer cannot get us
+	// to vouch for a lane it did not actually probe.
+	f.send(header.Test, header.LaneProbeAck, hostinfo.ConnectionState, hostinfo,
+		[]byte{lane, payload[1]}, rxc.nb, rxc.scratch[:0])
+}
+
+// handleLaneProbeAck promotes the lane a peer just acked.
+func (f *Interface) handleLaneProbeAck(hostinfo *HostInfo, payload []byte) {
+	ls := hostinfo.lanes
+	if ls == nil || len(payload) < 2 {
+		return
+	}
+
+	// The target is worth logging next to the demotion that names the same
+	// address, so a flapping lane can be read off the logs.
+	if target, promoted := ls.noteAck(int(payload[0]), payload[1], time.Now()); promoted {
+		hostinfo.logger(f.l).Info("Multiport lane up", "lane", payload[0], "udpAddr", target)
+	}
+}

lighthouse.go

@@ -36,6 +36,10 @@ type LightHouse struct {
 	myVpnNetworksTable *bart.Lite
 	punchy             *Punchy
 
+	// localAddrsFn enumerates the underlay addresses we advertise. It is a field so tests can supply simulated
+	// addresses rather than whatever this machine's NICs happen to be. Set it before Start.
+	localAddrsFn func(*LocalAllowList) []netip.Addr
+
 	// Local cache of answers from light houses
 	// map of vpn addr to answers
 	addrMap map[netip.Addr]*RemoteList
@@ -107,6 +111,10 @@ func NewLightHouseFromConfig(ctx context.Context, l *slog.Logger, c *config.C, c
 		queryChan:          make(chan netip.Addr, c.GetUint32("handshakes.query_buffer", 64)),
 		l:                  l,
 	}
+	h.localAddrsFn = func(al *LocalAllowList) []netip.Addr {
+		return localAddrs(h.l, al)
+	}
+
 	lighthouses := make([]netip.Addr, 0)
 	h.lighthouses.Store(&lighthouses)
 	staticList := make(map[netip.Addr]struct{})
@@ -918,7 +926,7 @@ func (lh *LightHouse) SendUpdate() {
 	}
 
 	lal := lh.GetLocalAllowList()
-	for _, e := range localAddrs(lh.l, lal) {
+	for _, e := range lh.localAddrsFn(lal) {
 		if lh.myVpnNetworksTable.Contains(e) {
 			continue
 		}

lighthouse_test.go

@@ -498,7 +498,7 @@ type testEncWriter struct {
 	protocolVersion cert.Version
 }
 
-func (tw *testEncWriter) SendVia(via *HostInfo, relay *Relay, ad, nb, out []byte, nocopy bool) {
+func (tw *testEncWriter) SendVia(via *HostInfo, relay *Relay, ad, nb, out []byte, nocopy bool, q int) {
 }
 func (tw *testEncWriter) Handshake(vpnIp netip.Addr) {
 }

main.go

@@ -4,13 +4,19 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
+	"math"
 	"net"
 	"net/netip"
+	"os"
 	"runtime/debug"
+	"slices"
 	"strings"
 	"time"
 
 	"github.com/slackhq/nebula/config"
+	"github.com/slackhq/nebula/cpupick"
+	"github.com/slackhq/nebula/header"
+	"github.com/slackhq/nebula/noiseutil"
 	"github.com/slackhq/nebula/overlay"
 	"github.com/slackhq/nebula/sshd"
 	"github.com/slackhq/nebula/udp"
@@ -20,6 +26,12 @@ import (
 
 type m = map[string]any
 
+// maxRoutines caps routines below the RejectHeadroom nonce gap so concurrent senders can't race the counter past wrap.
+const maxRoutines = 1 << 16
+
+// The reject headroom must exceed every sender that can be mid-reservation at once, about two per routine.
+const _ = noiseutil.RejectHeadroom - 4*maxRoutines
+
 func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, deviceFactory overlay.DeviceFactory) (retcon *Control, reterr error) {
 	ctx, cancel := context.WithCancel(context.Background())
 	// Automatically cancel the context if Main returns an error, to signal all created goroutines to quit.
@@ -33,6 +45,9 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 		buildVersion = moduleVersion()
 	}
 
+	// Debug builds (-tags debug) serve pprof on :6060; a no-op otherwise.
+	startPprofServer(ctx, l)
+
 	// Print the config if in test, the exit comes later
 	if configTest {
 		b, err := yaml.Marshal(c.Settings)
@@ -81,9 +96,6 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 		if routines < 1 {
 			routines = 1
 		}
-		if routines > 1 {
-			l.Info("Using multiple routines", "routines", routines)
-		}
 	} else {
 		// deprecated and undocumented
 		tunQueues := c.GetInt("tun.routines", 1)
@@ -93,6 +105,111 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 			l.Warn("Setting tun.routines and listen.routines is deprecated. Use `routines` instead", "routines", routines)
 		}
 	}
+	if routines > maxRoutines {
+		l.Warn("Using multiple routines", "routines", maxRoutines, "clamped", true, "requestedRoutines", routines)
+		routines = maxRoutines
+	} else if routines > 1 {
+		l.Info("Using multiple routines", "routines", routines)
+	}
+
+	port := c.GetInt("listen.port", 0)
+
+	batchSize := c.GetInt("listen.batch", 64)
+	if batchSize < 1 {
+		oldBatch := batchSize
+		batchSize = 1
+		l.Warn("listen.batch size is invalid", "provided", oldBatch, "overridden to", batchSize)
+	}
+	offloads := c.GetBool("listen.udp_offloads", false)
+
+	var listenHost netip.Addr
+	if !configTest {
+		rawListenHost := c.GetString("listen.host", "0.0.0.0")
+		if rawListenHost == "[::]" {
+			// Old guidance was to provide the literal `[::]` in `listen.host` but that won't resolve.
+			listenHost = netip.IPv6Unspecified()
+
+		} else {
+			ips, err := net.DefaultResolver.LookupNetIP(context.Background(), "ip", rawListenHost)
+			if err != nil {
+				return nil, util.ContextualizeIfNeeded("Failed to resolve listen.host", err)
+			}
+			if len(ips) == 0 {
+				return nil, util.ContextualizeIfNeeded("Failed to resolve listen.host", err)
+			}
+			listenHost = ips[0].Unmap()
+		}
+	}
+
+	// Multiport lanes: bind a range of consecutive UDP ports (listen.port+p)
+	// instead of SO_REUSEPORT-sharing one, and derive one extra session per lane
+	// with capable peers, so a tunnel's inside flows spread over several underlay
+	// 5-tuples instead of one. Defaults on, degrading gracefully when
+	// preconditions aren't met — managed deployments (dnclient) can't be
+	// hard-errored on config they don't control.
+	//
+	// `routines` is per port here rather than a total to divide up: every port
+	// gets its own full set, and a port's routines share it through SO_REUSEPORT
+	// so the kernel hashes each arriving 4-tuple onto one of them. That is what
+	// keeps a port from being served by a single core — the base port above all,
+	// since every handshake, every peer without multiport, and every tunnel whose
+	// lanes are down or firewalled arrives there. A routine still owns exactly one
+	// socket, which is what lets the read path own its state without locking, so
+	// the worker count is routines * ports and everything sized by routines from
+	// here down means that product.
+	routinesPerPort := routines
+	multiportPorts := 1
+	multiport := c.GetBool("multiport.enabled", true)
+	if multiport {
+		multiportPorts = c.GetInt("multiport.ports", 0)
+		if multiportPorts > header.MaxLane+1 {
+			// A lane index rides in one byte of the nebula header, so a port we
+			// could never address a lane on is a port we would never send from.
+			l.Warn("multiport.ports clamped to the lane header limit", "ports", multiportPorts, "limit", header.MaxLane+1)
+			multiportPorts = header.MaxLane + 1
+		}
+		if multiportPorts*routinesPerPort > maxRoutines {
+			clamped := max(maxRoutines/routinesPerPort, 1)
+			l.Warn("multiport.ports clamped to the routine limit",
+				"ports", multiportPorts, "clampedTo", clamped, "routinesPerPort", routinesPerPort, "limit", maxRoutines)
+			multiportPorts = clamped
+		}
+		if multiportPorts < 2 {
+			// A single port is a plain SO_REUSEPORT listener, which is what a node
+			// without multiport already runs. Say so rather than claiming lanes.
+			l.Info("multiport disabled: set multiport.ports > 1 to bind a lane port range")
+			multiport = false
+		}
+	}
+	if multiport && port != 0 && port+multiportPorts-1 > math.MaxUint16 {
+		l.Warn("multiport disabled: would bind ports beyond 65535", "listen.port", port, "ports", multiportPorts)
+		multiport = false
+	}
+	if multiport && !configTest {
+		// Every socket needs its own reader; a platform that can't run multiple
+		// readers would silently strand all but one of them as blackholes. Probe
+		// capability before sizing tun queues and routines to the port range.
+		probe, err := udp.NewListener(l, udp.Settings{
+			Listen: netip.AddrPortFrom(listenHost, 0),
+			Batch:  1,
+		})
+		if err != nil {
+			// We could not confirm support, so don't gamble a bound port range on it. The real bind below reports
+			// the underlying error if it is not transient.
+			l.Warn("multiport disabled: could not probe udp reader support", "error", err)
+			multiport = false
+		} else {
+			if !probe.SupportsMultipleReaders() {
+				l.Warn("multiport disabled: this platform does not support multiple udp readers")
+				multiport = false
+			}
+			_ = probe.Close()
+		}
+	}
+	if multiport {
+		routines = routinesPerPort * multiportPorts
+		l.Info("multiport routines", "ports", multiportPorts, "routinesPerPort", routinesPerPort, "routines", routines)
+	}
 
 	// EXPERIMENTAL
 	// Intentionally not documented yet while we do more testing and determine
@@ -128,44 +245,85 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 
 	// set up our UDP listener
 	udpConns := make([]udp.Conn, routines)
-	port := c.GetInt("listen.port", 0)
+
+	// Callers get no handle to these until the Control is returned, release them on any error.
+	defer func() {
+		if reterr != nil {
+			for _, u := range udpConns {
+				if u != nil {
+					_ = u.Close()
+				}
+			}
+		}
+	}()
 
 	if !configTest {
-		rawListenHost := c.GetString("listen.host", "0.0.0.0")
-		var listenHost netip.Addr
-		if rawListenHost == "[::]" {
-			// Old guidance was to provide the literal `[::]` in `listen.host` but that won't resolve.
-			listenHost = netip.IPv6Unspecified()
-
-		} else {
-			ips, err := net.DefaultResolver.LookupNetIP(context.Background(), "ip", rawListenHost)
-			if err != nil {
-				return nil, util.ContextualizeIfNeeded("Failed to resolve listen.host", err)
-			}
-			if len(ips) == 0 {
-				return nil, util.ContextualizeIfNeeded("Failed to resolve listen.host", err)
-			}
-			listenHost = ips[0].Unmap()
-		}
-
-		for i := 0; i < routines; i++ {
-			l.Info("listening", "addr", netip.AddrPortFrom(listenHost, uint16(port)))
-			udpServer, err := udp.NewListener(l, listenHost, port, routines > 1, c.GetInt("listen.batch", 64))
-			if err != nil {
-				return nil, util.NewContextualError("Failed to open udp listener", m{"queue": i}, err)
-			}
-			udpServer.ReloadConfig(c)
-			udpConns[i] = udpServer
-
-			// If port is dynamic, discover it before the next pass through the for loop
-			// This way all routines will use the same port correctly
-			if port == 0 {
-				uPort, err := udpServer.LocalAddr()
-				if err != nil {
-					return nil, util.NewContextualError("Failed to get listening port", nil, err)
+		// With a dynamic listen.port, multiport binds the first socket dynamically
+		// and then claims the next ports-1 above it; if that range turns out to be
+		// partially occupied, re-roll with a fresh dynamic port.
+		dynamic := port == 0
+		var bindErr error
+		for attempt := 0; attempt < 6; attempt++ {
+			bindErr = nil
+			for i := 0; i < routines; i++ {
+				// Routines are laid out port-major: routine i serves port slot
+				// i/routinesPerPort, so a port's routines are a contiguous run of
+				// indices and cpu pinning, which walks the index, spreads each
+				// port's group across the cores rather than stacking it on one.
+				slot := 0
+				if multiport {
+					slot = i / routinesPerPort
 				}
-				port = int(uPort.Port())
+				udpServer, err := udp.NewListener(l, udp.Settings{
+					Listen: netip.AddrPortFrom(listenHost, uint16(port+slot)),
+					// Under multiport the destination port narrows a packet to one
+					// port's routines and SO_REUSEPORT picks among them by 4-tuple
+					// hash, so both halves of the steering are load spreading: no
+					// port depends on a single core, and a lane still has a source
+					// port of its own to send from.
+					Multi:    routines > 1,
+					Batch:    batchSize,
+					Offloads: offloads,
+				})
+				if err != nil {
+					bindErr = util.NewContextualError("Failed to open udp listener", m{"queue": i}, err)
+					break
+				}
+				udpServer.ReloadConfig(c)
+				udpConns[i] = udpServer
+
+				// If port is dynamic, discover it before the next pass through the for loop
+				// This way all routines will use the same port correctly
+				if port == 0 {
+					uPort, err := udpServer.LocalAddr()
+					if err != nil {
+						return nil, util.NewContextualError("Failed to get listening port", nil, err)
+					}
+					port = int(uPort.Port())
+					if multiport && port+multiportPorts-1 > math.MaxUint16 {
+						bindErr = util.NewContextualError("multiport dynamic port too close to 65535", m{"port": port}, nil)
+						break
+					}
+				}
+				l.Info("listening", "addr", netip.AddrPortFrom(listenHost, uint16(port+slot)), "socket", i)
 			}
+			if bindErr == nil {
+				break
+			}
+			if !(multiport && dynamic) {
+				return nil, bindErr
+			}
+			for i := range udpConns {
+				if udpConns[i] != nil {
+					_ = udpConns[i].Close()
+					udpConns[i] = nil
+				}
+			}
+			port = 0
+			l.Debug("multiport dynamic port range collided, retrying", "attempt", attempt+1)
+		}
+		if bindErr != nil {
+			return nil, bindErr
 		}
 	}
 
@@ -191,6 +349,26 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 		messageMetrics: messageMetrics,
 	}
 
+	if multiport {
+		// A lane needs a port to send from, so we can send on no more lanes than we
+		// bound ports. multiport.lanes below that sends on a subset of the range,
+		// which is only interesting for narrowing an experiment: the ports are bound
+		// and read either way.
+		lanes := c.GetInt("multiport.lanes", 0)
+		if lanes <= 0 || lanes > multiportPorts {
+			lanes = multiportPorts
+		}
+		handshakeConfig.laneCount = lanes
+		handshakeConfig.lanePortCount = uint16(multiportPorts)
+		handshakeConfig.laneBasePort = uint16(port)
+
+		// Every other multiport log line is a reason it turned itself off, so say
+		// plainly when it is on and with what. A peer only gets lanes if it also
+		// advertises a port range, so this is our half of the negotiation.
+		l.Info("multiport enabled", "lanes", lanes, "basePort", port, "ports", multiportPorts,
+			"routinesPerPort", routinesPerPort)
+	}
+
 	handshakeManager := NewHandshakeManager(l, hostMap, lightHouse, udpConns[0], handshakeConfig)
 	lightHouse.handshakeTrigger = handshakeManager.trigger
 
@@ -199,6 +377,37 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 		l.Warn("Failed to start DNS responder", "error", err)
 	}
 
+	pinThreads := c.GetBool("tun.pin_threads", true)
+	cpuAffinity := parseCpuAffinity(c, l, routines)
+	if pinThreads && routines > 1 && len(cpuAffinity) == 0 && !configTest {
+		// The operator didn't choose pin CPUs, so pick a default set that
+		// prefers performance cores and doesn't stack co-located instances
+		// onto allowed[0].
+
+		// key is used to seed the spreading of routines->cores.
+		// use PID if you want to ensure many different Nebulas in VMs or containers land on different cores
+		// use port if you want to always end up on the same cores, ideal for benchmarking.
+		key := uint64(os.Getpid()) //default to PID
+		pinKeyStr := strings.ToLower(c.GetString("tun.pin_threads_key", ""))
+		switch pinKeyStr {
+		case "":
+			l.Debug("tun.pin_threads_key is empty, using PID")
+		case "pid":
+			l.Debug("tun.pin_threads_key is PID")
+		case "port":
+			if ap, err := udpConns[0].LocalAddr(); err == nil && ap.Port() != 0 {
+				l.Info("tun.pin_threads_key is port number")
+				key = uint64(ap.Port())
+			} else {
+				l.Warn("Failed to get a port number for tun.pin_threads_key, falling back to PID", "err", err)
+			}
+		default:
+			l.Warn("tun.pin_threads_key is invalid, using PID")
+		}
+
+		cpuAffinity = cpupick.Default(routines, key, l)
+	}
+
 	ifConfig := &InterfaceConfig{
 		HostMap:               hostMap,
 		Inside:                tun,
@@ -215,11 +424,16 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 		DropLocalBroadcast:    c.GetBool("tun.drop_local_broadcast", false),
 		DropMulticast:         c.GetBool("tun.drop_multicast", false),
 		routines:              routines,
+		Multiport:             multiport,
+		RoutinesPerPort:       routinesPerPort,
+		LaneCount:             handshakeConfig.laneCount,
 		MessageMetrics:        messageMetrics,
 		version:               buildVersion,
 		relayManager:          NewRelayManager(ctx, l, hostMap, c),
 		punchy:                punchy,
 		ConntrackCacheTimeout: conntrackCacheTimeout,
+		CpuAffinity:           cpuAffinity,
+		PinThreads:            pinThreads,
 		l:                     l,
 	}
 
@@ -257,6 +471,8 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 
 	attachCommands(l, c, ssh, ifce)
 
+	networkChanges := udp.NewNetworkChangeMonitor(ctx, l, c)
+
 	return &Control{
 		state:                  StateReady,
 		f:                      ifce,
@@ -267,10 +483,75 @@ func Main(c *config.C, configTest bool, buildVersion string, l *slog.Logger, dev
 		statsStart:             stats.Start,
 		dnsStart:               ds.Start,
 		lighthouseStart:        lightHouse.StartUpdateWorker,
+		networkChangeStart:     networkChanges.Start,
 		connectionManagerStart: connManager.Start,
 	}, nil
 }
 
+// parseCpuAffinity reads `tun.cpu_affinity` from the config — a list of
+// integer CPU IDs, one per TUN reader goroutine. Empty / unset returns nil
+// (listenIn falls back to spreading queues across the allowed CPU set).
+// Length mismatch with `routines` is a warning, not an error: shorter lists
+// are modulo-cycled across queues, longer lists' tail is ignored. Invalid
+// entries (non-integer, or a CPU ID we're not allowed to run on) are also a
+// warning and disable the override entirely so we don't silently pin to the
+// wrong CPU. Entries are validated against the process's current affinity
+// mask (util.AllowedCPUs) rather than 0..NumCPU-1: under a cgroup cpuset or
+// taskset the runnable IDs are frequently not that contiguous range, and
+// pinning to an unrunnable ID always fails. If the allowed set can't be
+// determined we fall back to a plain non-negative check.
+func parseCpuAffinity(c *config.C, l *slog.Logger, routines int) []int {
+	raw := c.Get("tun.cpu_affinity")
+	if raw == nil {
+		return nil
+	}
+	rv, ok := raw.([]any)
+	if !ok {
+		l.Warn("tun.cpu_affinity must be a list of integers; ignoring", "value", raw)
+		return nil
+	}
+	// allowed is the set of CPU IDs we're actually permitted to run on. A nil
+	// slice (unsupported platform or lookup error) means "can't tell", so we
+	// only apply the weaker non-negative check in that case.
+	allowed, err := util.AllowedCPUs()
+	if err != nil {
+		l.Warn("could not determine allowed CPUs; validating tun.cpu_affinity against non-negative only", "error", err)
+		allowed = nil
+	}
+	cpus := make([]int, 0, len(rv))
+	for i, e := range rv {
+		var cpu int
+		switch v := e.(type) {
+		case int:
+			cpu = v
+		case int64:
+			cpu = int(v)
+		case float64:
+			cpu = int(v)
+		default:
+			l.Warn("tun.cpu_affinity entry not an integer; ignoring affinity",
+				"index", i, "value", e)
+			return nil
+		}
+		if cpu < 0 {
+			l.Warn("tun.cpu_affinity entry out of range; ignoring affinity",
+				"index", i, "cpu", cpu)
+			return nil
+		}
+		if len(allowed) > 0 && !slices.Contains(allowed, cpu) {
+			l.Warn("tun.cpu_affinity entry not in allowed CPU set; ignoring affinity",
+				"index", i, "cpu", cpu, "allowed", allowed)
+			return nil
+		}
+		cpus = append(cpus, cpu)
+	}
+	if len(cpus) != routines {
+		l.Warn("tun.cpu_affinity length doesn't match routines; queues will modulo-cycle through the list",
+			"affinity_len", len(cpus), "routines", routines)
+	}
+	return cpus
+}
+
 func moduleVersion() string {
 	info, ok := debug.ReadBuildInfo()
 	if !ok {

main_test.go

@@ -0,0 +1,51 @@
+package nebula
+
+import (
+	"testing"
+
+	"github.com/slackhq/nebula/config"
+	"github.com/slackhq/nebula/test"
+	"github.com/slackhq/nebula/util"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseCpuAffinity(t *testing.T) {
+	l := test.NewLogger()
+
+	// newConfig returns a config.C with tun.cpu_affinity set to v. A nil v
+	// leaves the key unset.
+	newConfig := func(v any) *config.C {
+		c := config.NewC(l)
+		if v != nil {
+			c.Settings["tun"] = map[string]any{"cpu_affinity": v}
+		}
+		return c
+	}
+
+	// unset -> nil (listenIn falls back to spreading across the allowed set)
+	assert.Nil(t, parseCpuAffinity(newConfig(nil), l, 1))
+
+	// Pick a CPU we're actually allowed to run on so a valid list survives
+	// validation regardless of the host's affinity mask.
+	allowed, _ := util.AllowedCPUs()
+	validCPU := 0
+	if len(allowed) > 0 {
+		validCPU = allowed[0]
+	}
+
+	// valid list -> parsed through unchanged
+	assert.Equal(t, []int{validCPU, validCPU}, parseCpuAffinity(newConfig([]any{validCPU, validCPU}), l, 2))
+
+	// a negative entry is out of range on every platform -> disables the override
+	assert.Nil(t, parseCpuAffinity(newConfig([]any{validCPU, -1}), l, 2))
+
+	// a non-integer entry -> disables the override
+	assert.Nil(t, parseCpuAffinity(newConfig([]any{validCPU, "not-a-cpu"}), l, 2))
+
+	// a CPU id outside the allowed set -> disables the override. Only assertable
+	// where we can enumerate the allowed set (e.g. linux); 1<<20 is far beyond
+	// any representable CPU id so it can never be in the mask.
+	if len(allowed) > 0 {
+		assert.Nil(t, parseCpuAffinity(newConfig([]any{1 << 20}), l, 1))
+	}
+}

message_metrics.go

@@ -14,7 +14,8 @@ type MessageMetrics struct {
 	rxUnknown metrics.Counter
 	txUnknown metrics.Counter
 
-	rxInvalid metrics.Counter
+	rxInvalid   metrics.Counter
+	txExhausted metrics.Counter
 }
 
 func (m *MessageMetrics) Rx(t header.MessageType, s header.MessageSubType, i int64) {
@@ -41,6 +42,13 @@ func (m *MessageMetrics) RxInvalid(i int64) {
 	}
 }
 
+// TxExhausted counts outbound packets dropped because the tunnel's message counter is spent.
+func (m *MessageMetrics) TxExhausted(i int64) {
+	if m != nil && m.txExhausted != nil {
+		m.txExhausted.Inc(i)
+	}
+}
+
 func newMessageMetrics() *MessageMetrics {
 	gen := func(t string) [][]metrics.Counter {
 		return [][]metrics.Counter{
@@ -61,9 +69,10 @@ func newMessageMetrics() *MessageMetrics {
 		rx: gen("rx"),
 		tx: gen("tx"),
 
-		rxUnknown: metrics.GetOrRegisterCounter("messages.rx.other", nil),
-		txUnknown: metrics.GetOrRegisterCounter("messages.tx.other", nil),
-		rxInvalid: metrics.GetOrRegisterCounter("messages.rx.invalid", nil),
+		rxUnknown:   metrics.GetOrRegisterCounter("messages.rx.other", nil),
+		txUnknown:   metrics.GetOrRegisterCounter("messages.tx.other", nil),
+		rxInvalid:   metrics.GetOrRegisterCounter("messages.rx.invalid", nil),
+		txExhausted: metrics.GetOrRegisterCounter("messages.tx.exhausted", nil),
 	}
 }
 

noiseutil/aesgcm.go

@@ -25,6 +25,9 @@ func (s *CipherStateAESGCM) EncryptDanger(out, ad, plaintext []byte, n uint64, n
 	if s == nil {
 		return nil, errors.New("no cipher state available to encrypt")
 	}
+	if n >= RejectAfterMessages {
+		return nil, ErrMessageCounterExhausted
+	}
 	nb[0] = 0
 	nb[1] = 0
 	nb[2] = 0

noiseutil/boring.go

@@ -4,77 +4,16 @@
 package noiseutil
 
 import (
-	"crypto/aes"
-	"crypto/cipher"
-	"encoding/binary"
-
-	// unsafe needed for go:linkname
-	_ "unsafe"
+	"crypto/boring"
 
 	"github.com/flynn/noise"
 )
 
+var CipherAESGCM noise.CipherFunc = CipherAESGCMFIPS140
+
 // EncryptLockNeeded indicates if calls to Encrypt need a lock
 // This is true for boringcrypto because the Seal function verifies that the
 // nonce is strictly increasing.
 const EncryptLockNeeded = true
 
-// NewGCMTLS is no longer exposed in go1.19+, so we need to link it in
-// See: https://github.com/golang/go/issues/56326
-//
-// NewGCMTLS is the internal method used with boringcrypto that provides a
-// validated mode of AES-GCM which enforces the nonce is strictly
-// monotonically increasing.  This is the TLS 1.2 specification for nonce
-// generation (which also matches the method used by the Noise Protocol)
-//
-// - https://github.com/golang/go/blob/go1.19/src/crypto/tls/cipher_suites.go#L520-L522
-// - https://github.com/golang/go/blob/go1.19/src/crypto/internal/boring/aes.go#L235-L237
-// - https://github.com/golang/go/blob/go1.19/src/crypto/internal/boring/aes.go#L250
-// - https://github.com/google/boringssl/blob/ae223d6138807a13006342edfeef32e813246b39/include/openssl/aead.h#L379-L381
-// - https://github.com/google/boringssl/blob/ae223d6138807a13006342edfeef32e813246b39/crypto/fipsmodule/cipher/e_aes.c#L1082-L1093
-//
-//go:linkname newGCMTLS crypto/internal/boring.NewGCMTLS
-func newGCMTLS(c cipher.Block) (cipher.AEAD, error)
-
-type cipherFn struct {
-	fn   func([32]byte) noise.Cipher
-	name string
-}
-
-func (c cipherFn) Cipher(k [32]byte) noise.Cipher { return c.fn(k) }
-func (c cipherFn) CipherName() string             { return c.name }
-
-// CipherAESGCM is the AES256-GCM AEAD cipher (using NewGCMTLS when GoBoring is present)
-var CipherAESGCM noise.CipherFunc = cipherFn{cipherAESGCMBoring, "AESGCM"}
-
-func cipherAESGCMBoring(k [32]byte) noise.Cipher {
-	c, err := aes.NewCipher(k[:])
-	if err != nil {
-		panic(err)
-	}
-	gcm, err := newGCMTLS(c)
-	if err != nil {
-		panic(err)
-	}
-	return aeadCipher{
-		gcm,
-		func(n uint64) []byte {
-			var nonce [12]byte
-			binary.BigEndian.PutUint64(nonce[4:], n)
-			return nonce[:]
-		},
-	}
-}
-
-type aeadCipher struct {
-	cipher.AEAD
-	nonce func(uint64) []byte
-}
-
-func (c aeadCipher) Encrypt(out []byte, n uint64, ad, plaintext []byte) []byte {
-	return c.Seal(out, c.nonce(n), plaintext, ad)
-}
-
-func (c aeadCipher) Decrypt(out []byte, n uint64, ad, ciphertext []byte) ([]byte, error) {
-	return c.Open(out, c.nonce(n), ciphertext, ad)
-}
+var boringEnabled = boring.Enabled()

noiseutil/boring_test.go

@@ -4,8 +4,6 @@
 package noiseutil
 
 import (
-	"crypto/boring"
-	"encoding/hex"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -14,33 +12,3 @@ import (
 func TestEncryptLockNeeded(t *testing.T) {
 	assert.True(t, EncryptLockNeeded)
 }
-
-// Ensure NewGCMTLS validates the nonce is non-repeating
-func TestNewGCMTLS(t *testing.T) {
-	assert.True(t, boring.Enabled())
-
-	// Test Case 16 from GCM Spec:
-	//  - (now dead link): http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf
-	//  - as listed in boringssl tests: https://github.com/google/boringssl/blob/fips-20220613/crypto/cipher_extra/test/cipher_tests.txt#L412-L418
-	key, _ := hex.DecodeString("feffe9928665731c6d6a8f9467308308feffe9928665731c6d6a8f9467308308")
-	iv, _ := hex.DecodeString("cafebabefacedbaddecaf888")
-	plaintext, _ := hex.DecodeString("d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39")
-	aad, _ := hex.DecodeString("feedfacedeadbeeffeedfacedeadbeefabaddad2")
-	expected, _ := hex.DecodeString("522dc1f099567d07f47f37a32a84427d643a8cdcbfe5c0c97598a2bd2555d1aa8cb08e48590dbb3da7b08b1056828838c5f61e6393ba7a0abcc9f662")
-	expectedTag, _ := hex.DecodeString("76fc6ece0f4e1768cddf8853bb2d551b")
-
-	expected = append(expected, expectedTag...)
-
-	var keyArray [32]byte
-	copy(keyArray[:], key)
-	c := CipherAESGCM.Cipher(keyArray)
-	aead := c.(aeadCipher).AEAD
-
-	dst := aead.Seal([]byte{}, iv, plaintext, aad)
-	assert.Equal(t, expected, dst)
-
-	// We expect this to fail since we are re-encrypting with a repeat IV
-	assert.PanicsWithError(t, "boringcrypto: EVP_AEAD_CTX_seal failed", func() {
-		dst = aead.Seal([]byte{}, iv, plaintext, aad)
-	})
-}

noiseutil/chachapoly.go

@@ -24,6 +24,9 @@ func (s *CipherStateChaChaPoly) EncryptDanger(out, ad, plaintext []byte, n uint6
 	if s == nil {
 		return nil, errors.New("no cipher state available to encrypt")
 	}
+	if n >= RejectAfterMessages {
+		return nil, ErrMessageCounterExhausted
+	}
 	nb[0] = 0
 	nb[1] = 0
 	nb[2] = 0

noiseutil/cipher_state.go

@@ -1,11 +1,23 @@
 package noiseutil
 
 import (
+	"crypto/cipher"
+	"errors"
 	"fmt"
+	"math"
 
 	"github.com/flynn/noise"
 )
 
+// RejectHeadroom is the wrap gap for senders racing the counter, sized large enough for any routine count.
+const RejectHeadroom = uint64(1) << 40
+
+// RejectAfterMessages is the nonce ceiling: encrypting stops RejectHeadroom short of the wrap.
+const RejectAfterMessages = math.MaxUint64 - RejectHeadroom
+
+// ErrMessageCounterExhausted is returned by EncryptDanger once the nonce reaches RejectAfterMessages.
+var ErrMessageCounterExhausted = errors.New("message counter exhausted")
+
 // CipherState is the post-handshake AEAD cipher used for the data plane.
 // Each supported cipher has its own concrete implementation in this package with the nonce endianness hardcoded,
 // so the encrypt/decrypt fast path avoids interface dispatch on the byte order.
@@ -29,8 +41,11 @@ type CipherState interface {
 // NewCipherState wraps the post-handshake noise.CipherState in the per-cipher type that matches cipherFunc.
 // cipherFunc must be the same cipher used to build the noise CipherSuite that produced s.
 func NewCipherState(s *noise.CipherState, cipherFunc noise.CipherFunc) CipherState {
+	if cs, ok := s.Cipher().(CipherState); ok {
+		return cs
+	}
 	switch cipherFunc.CipherName() {
-	case CipherAESGCM.CipherName():
+	case noise.CipherAESGCM.CipherName():
 		return NewCipherStateAESGCM(s)
 	case noise.CipherChaChaPoly.CipherName():
 		return NewCipherStateChaChaPoly(s)
@@ -38,3 +53,29 @@ func NewCipherState(s *noise.CipherState, cipherFunc noise.CipherFunc) CipherSta
 		panic(fmt.Sprintf("noiseutil: unsupported cipher %q", cipherFunc.CipherName()))
 	}
 }
+
+// NewCipherStateFromKey builds a data-plane CipherState directly from raw key
+// bytes, bypassing the noise handshake. Multiport lanes use this to key a
+// derived session off the base tunnel's negotiated keys; the caller owns the
+// guarantee that key is used with exactly one CipherState so nonces never
+// repeat.
+func NewCipherStateFromKey(key [32]byte, cipherFunc noise.CipherFunc) CipherState {
+	c := cipherFunc.Cipher(key)
+	if cs, ok := c.(CipherState); ok {
+		return cs
+	}
+
+	aead, ok := c.(cipher.AEAD)
+	if !ok {
+		panic(fmt.Sprintf("noiseutil: cipher %q does not expose an AEAD", cipherFunc.CipherName()))
+	}
+
+	switch cipherFunc.CipherName() {
+	case noise.CipherAESGCM.CipherName():
+		return &CipherStateAESGCM{c: aead}
+	case noise.CipherChaChaPoly.CipherName():
+		return &CipherStateChaChaPoly{c: aead}
+	default:
+		panic(fmt.Sprintf("noiseutil: unsupported cipher %q", cipherFunc.CipherName()))
+	}
+}

noiseutil/cipher_state_test.go

@@ -1,6 +1,8 @@
 package noiseutil
 
 import (
+	"crypto/fips140"
+	"math"
 	"testing"
 
 	"github.com/flynn/noise"
@@ -10,24 +12,30 @@ import (
 
 func TestCipherStateAESGCMRoundtrip(t *testing.T) {
 	enc, dec := buildCipherStates(t, CipherAESGCM)
-	roundtrip(t, NewCipherStateAESGCM(enc), NewCipherStateAESGCM(dec))
+	roundtrip(t, NewCipherState(enc, CipherAESGCM), NewCipherState(dec, CipherAESGCM))
 }
 
 func TestCipherStateChaChaPolyRoundtrip(t *testing.T) {
 	enc, dec := buildCipherStates(t, noise.CipherChaChaPoly)
-	roundtrip(t, NewCipherStateChaChaPoly(enc), NewCipherStateChaChaPoly(dec))
+	roundtrip(t, NewCipherState(enc, noise.CipherChaChaPoly), NewCipherState(dec, noise.CipherChaChaPoly))
 }
 
 func TestNewCipherStateDispatch(t *testing.T) {
 	encA, _ := buildCipherStates(t, CipherAESGCM)
 	encC, _ := buildCipherStates(t, noise.CipherChaChaPoly)
 
-	assert.IsType(t, &CipherStateAESGCM{}, NewCipherState(encA, CipherAESGCM))
+	if !boringEnabled && !fips140.Enabled() {
+		assert.IsType(t, &CipherStateAESGCM{}, NewCipherState(encA, CipherAESGCM))
+	} else {
+		// fips140
+		assert.IsType(t, encA.Cipher(), NewCipherState(encA, CipherAESGCM))
+	}
+
 	assert.IsType(t, &CipherStateChaChaPoly{}, NewCipherState(encC, noise.CipherChaChaPoly))
 }
 
 func TestNewCipherStateUnsupportedPanics(t *testing.T) {
-	enc, _ := buildCipherStates(t, CipherAESGCM)
+	enc, _ := buildCipherStates(t, noise.CipherChaChaPoly)
 	assert.Panics(t, func() {
 		NewCipherState(enc, fakeCipher{})
 	})
@@ -89,6 +97,24 @@ func roundtrip(t *testing.T, enc, dec CipherState) {
 	assert.Equal(t, 16, enc.Overhead())
 }
 
+func TestEncryptRejectsExhaustedCounter(t *testing.T) {
+	// Pin the headroom below the uint64 wrap so a typo can't silently move the ceiling.
+	require.Equal(t, uint64(1)<<40, RejectHeadroom)
+	require.Equal(t, math.MaxUint64-RejectHeadroom, RejectAfterMessages)
+
+	encA, _ := buildCipherStates(t, CipherAESGCM)
+	encC, _ := buildCipherStates(t, noise.CipherChaChaPoly)
+	nb := make([]byte, 12)
+
+	for _, cs := range []CipherState{NewCipherStateAESGCM(encA), NewCipherStateChaChaPoly(encC)} {
+		_, err := cs.EncryptDanger(nil, nil, []byte("x"), RejectAfterMessages-1, nb)
+		require.NoError(t, err)
+
+		_, err = cs.EncryptDanger(nil, nil, []byte("x"), RejectAfterMessages, nb)
+		require.ErrorIs(t, err, ErrMessageCounterExhausted)
+	}
+}
+
 func BenchmarkCipherStateEncryptAESGCM(b *testing.B) {
 	enc, _ := buildCipherStatesB(b, CipherAESGCM)
 	benchEncryptCipherState(b, NewCipherState(enc, CipherAESGCM))
@@ -164,3 +190,48 @@ func TestCipherStateNilSafety(t *testing.T) {
 	assert.Empty(t, out)
 	assert.Equal(t, 0, cc.Overhead())
 }
+
+func TestCipherStateAESGCMInPlaceDecrypt(t *testing.T) {
+	enc, dec := buildCipherStates(t, CipherAESGCM)
+	inPlaceDecrypt(t, NewCipherStateAESGCM(enc), NewCipherStateAESGCM(dec))
+}
+
+func TestCipherStateChaChaPolyInPlaceDecrypt(t *testing.T) {
+	enc, dec := buildCipherStates(t, noise.CipherChaChaPoly)
+	inPlaceDecrypt(t, NewCipherStateChaChaPoly(enc), NewCipherStateChaChaPoly(dec))
+}
+
+func inPlaceDecrypt(t *testing.T, enc, dec CipherState) {
+	t.Helper()
+	const hdrLen = 16
+	plaintext := []byte("in-place decrypt should replace the ciphertext bytes")
+	nb := make([]byte, 12)
+
+	// packet = [16-byte header | ciphertext+tag], like a nebula Message.
+	packet := make([]byte, hdrLen, hdrLen+len(plaintext)+enc.Overhead())
+	for i := range packet {
+		packet[i] = byte(i)
+	}
+	packet, err := enc.EncryptDanger(packet, packet[:hdrLen], plaintext, 1, nb)
+	require.NoError(t, err)
+
+	// Simulate a GRO row: [packet | next segment]. A failed auth on packet
+	// may zero packet's plaintext region but must not touch the header, the
+	// tag, or the neighboring segment.
+	neighbor := []byte("next coalesced segment, must stay intact")
+	row := append(append([]byte(nil), packet...), neighbor...)
+	tampered := row[:len(packet)]
+	tampered[hdrLen] ^= 0x01
+	_, err = dec.DecryptDanger(tampered[hdrLen:hdrLen], tampered[:hdrLen], tampered[hdrLen:], 1, nb)
+	require.Error(t, err)
+	assert.Equal(t, packet[:hdrLen], tampered[:hdrLen], "failed auth must not touch the header")
+	assert.Equal(t, packet[len(packet)-dec.Overhead():], tampered[len(tampered)-dec.Overhead():],
+		"failed auth must not touch the tag")
+	assert.Equal(t, neighbor, row[len(packet):], "failed auth must not touch the next segment")
+
+	out, err := dec.DecryptDanger(packet[hdrLen:hdrLen], packet[:hdrLen], packet[hdrLen:], 1, nb)
+	require.NoError(t, err)
+	assert.Equal(t, plaintext, out)
+	// The plaintext must be IN the packet buffer, not a fresh allocation.
+	assert.Equal(t, &packet[hdrLen], &out[0], "plaintext must alias the packet buffer")
+}

noiseutil/fips140.go

@@ -0,0 +1,197 @@
+package noiseutil
+
+import (
+	"bytes"
+	"crypto/cipher"
+	"crypto/fips140"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"reflect"
+	"runtime"
+	"unsafe"
+
+	// unsafe needed for go:linkname
+	_ "crypto/tls"
+	_ "unsafe"
+
+	"github.com/flynn/noise"
+)
+
+// TODO: Use NewGCMWithCounterNonce or NewGCMForQUIC once available:
+// - https://github.com/golang/go/issues/73110
+// - https://github.com/golang/go/issues/79219
+// Using tls.aeadAESGCMTLS13 gives us the TLS 1.3 GCM, which also verifies
+// that the nonce is strictly increasing. This works for both boringcrypto
+// and fips140.
+//
+//go:linkname aeadAESGCMTLS13 crypto/tls.aeadAESGCMTLS13
+func aeadAESGCMTLS13(key, noncePrefix []byte) cipher.AEAD
+
+type cipherFn struct {
+	fn   func([32]byte) noise.Cipher
+	name string
+}
+
+func (c cipherFn) Cipher(k [32]byte) noise.Cipher { return c.fn(k) }
+func (c cipherFn) CipherName() string             { return c.name }
+
+// CipherAESGCMFIPS140 is the AES256-GCM AEAD cipher (using tls.aeadAESGCMTLS13, for both boringcrypto and fips140)
+var CipherAESGCMFIPS140 noise.CipherFunc = cipherFn{cipherAESGCMFIPS140, "AESGCM"}
+
+// tls.aeadAESGCMTLS13 uses a 4 byte static prefix and an 8 byte XOR mask
+var emptyNonce = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+
+func cipherAESGCMFIPS140(k [32]byte) noise.Cipher {
+	gcm := aeadAESGCMTLS13(k[:], emptyNonce)
+	gcm = extractFIPSAEAD(gcm)
+	return &aeadGCMFIPS140Cipher{
+		AEAD: gcm,
+	}
+}
+
+type aeadGCMFIPS140Cipher struct {
+	cipher.AEAD
+	ready bool
+}
+
+// Extract the internal FIPS GCM implementation from the tls wrapper. The TLS
+// wrapper is not thread safe around Open, so instead of locking around it we
+// can grab the internal implementation that is thread safe. This is the FIPS
+// module implementation: `crypto/internal/fips140/aes/gcm.GCMWithXORCounterNonce`
+//
+// - https://github.com/golang/go/blob/go1.26.4/src/crypto/internal/fips140/aes/gcm/gcm_nonces.go#L212-L287
+//
+// The wrapper is struct `crypto/tls.xorNonceAEAD` , with field `aead`:
+//
+// - https://github.com/golang/go/blob/go1.26.4/src/crypto/tls/cipher_suites.go#L482-L487
+//
+// This can be cleaned up once these FIPS implementations are exposed directly:
+//
+// - https://github.com/golang/go/issues/73110
+func extractFIPSAEAD(xorNonceAEAD cipher.AEAD) cipher.AEAD {
+	r := reflect.ValueOf(xorNonceAEAD)
+	v := r.Elem().FieldByName("aead")
+	if !v.IsValid() {
+		// The internal crypto/tls.xorNonceAEAD struct no longer has an `aead`
+		// field. This can only happen on a Go version this code was not built
+		// against; the package init() self-test guards against ever reaching
+		// this at runtime, so this is a defensive fail-fast.
+		panic(fmt.Sprintf("noiseutil: could not extract FIPS AEAD from %T on %s: no `aead` field (incompatible Go version)", xorNonceAEAD, runtime.Version()))
+	}
+	v2 := reflect.NewAt(v.Type(), unsafe.Pointer(v.UnsafeAddr())).Elem()
+	aead, ok := v2.Interface().(cipher.AEAD)
+	if !ok {
+		panic(fmt.Sprintf("noiseutil: extracted FIPS `aead` field is %s, not a cipher.AEAD, on %s (incompatible Go version)", v2.Type(), runtime.Version()))
+	}
+	return aead
+}
+
+func (c *aeadGCMFIPS140Cipher) init(nonce []byte) {
+	// GCMWithXORCounterNonce expects that the first call to Seal
+	// is with a counter of `0`, this is how it extracts the nonce mask.
+	// We can clean this up in the future when NewGCMWithCounterNonce or
+	// NewGCMForQUIC are available:
+	if !bytes.Equal(emptyNonce, nonce) {
+		c.AEAD.Seal([]byte{}, emptyNonce, []byte{}, []byte{})
+	}
+	c.ready = true
+}
+
+func (c *aeadGCMFIPS140Cipher) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
+	if !c.ready {
+		c.init(nonce)
+	}
+	return c.AEAD.Seal(dst, nonce, plaintext, additionalData)
+}
+
+func (c *aeadGCMFIPS140Cipher) Encrypt(out []byte, n uint64, ad, plaintext []byte) []byte {
+	return c.Seal(out, aeadGCMFIPS140CipherNonce(n), plaintext, ad)
+}
+
+func (c *aeadGCMFIPS140Cipher) Decrypt(out []byte, n uint64, ad, ciphertext []byte) ([]byte, error) {
+	return c.Open(out, aeadGCMFIPS140CipherNonce(n), ciphertext, ad)
+}
+
+func (c *aeadGCMFIPS140Cipher) EncryptDanger(out, ad, plaintext []byte, n uint64, nb []byte) ([]byte, error) {
+	if c == nil {
+		return nil, errors.New("no cipher state available to encrypt")
+	}
+	if n >= RejectAfterMessages {
+		return nil, ErrMessageCounterExhausted
+	}
+	binary.BigEndian.PutUint64(nb[4:], n)
+	out = c.Seal(out, nb, plaintext, ad)
+	return out, nil
+}
+
+func (c *aeadGCMFIPS140Cipher) DecryptDanger(out, ad, ciphertext []byte, n uint64, nb []byte) ([]byte, error) {
+	if c == nil {
+		return []byte{}, nil
+	}
+	binary.BigEndian.PutUint64(nb[4:], n)
+	return c.Open(out, nb, ciphertext, ad)
+}
+
+func (c *aeadGCMFIPS140Cipher) Overhead() int {
+	if c == nil {
+		return 0
+	}
+	return c.AEAD.Overhead()
+}
+
+func aeadGCMFIPS140CipherNonce(n uint64) []byte {
+	// GCMWithXORCounterNonce uses a 4 byte static prefix and an 8 byte nonce
+	var nonce [12]byte
+	binary.BigEndian.PutUint64(nonce[4:], n)
+	return nonce[:]
+}
+
+func init() {
+	if boringEnabled || fips140.Enabled() {
+		initSelfTestAESGCMFIPS140()
+	}
+}
+
+// validates the go:linkname + reflection extraction and the nonce-reuse
+// protection at startup. cipherAESGCMFIPS140 relies on unexported
+// crypto/tls and crypto/internal/fips140 internals; if a future Go version changes
+// those, this fails fast with a clear message instead of panicking per-handshake
+// (or, worse, silently losing the strictly-increasing nonce check that is the whole
+// point of using this cipher).
+func initSelfTestAESGCMFIPS140() {
+	var key [32]byte
+	c := cipherAESGCMFIPS140(key)
+
+	// Verify the extracted AEAD produces a working encrypt/decrypt roundtrip.
+	plaintext := []byte("nebula fips140 self-test")
+	ad := []byte("ad")
+	ct := c.Encrypt(nil, 1, ad, plaintext)
+	pt, err := c.Decrypt(nil, 1, ad, ct)
+	if err != nil {
+		panic(fmt.Sprintf("noiseutil: FIPS AES-GCM self-test roundtrip failed on %s: %v", runtime.Version(), err))
+	}
+	if !bytes.Equal(pt, plaintext) {
+		panic(fmt.Sprintf("noiseutil: FIPS AES-GCM self-test roundtrip returned wrong plaintext on %s", runtime.Version()))
+	}
+
+	// Verify the nonce-reuse protection still fires: re-encrypting with the same
+	// counter must panic. This is the defensive check that FIPS-140 requires, so
+	// if the extraction ever silently yields an AEAD without it, refuse to start.
+	if !reusePanics(c) {
+		panic(fmt.Sprintf("noiseutil: FIPS AES-GCM self-test did not reject a reused nonce on %s; nonce-reuse protection is missing (incompatible Go version)", runtime.Version()))
+	}
+}
+
+// reusePanics reports whether re-encrypting with an already-used counter panics,
+// as GCMWithXORCounterNonce is expected to.
+func reusePanics(c noise.Cipher) (panicked bool) {
+	c.Encrypt(nil, 2, nil, nil)
+	defer func() {
+		if recover() != nil {
+			panicked = true
+		}
+	}()
+	c.Encrypt(nil, 2, nil, nil)
+	return false
+}

noiseutil/fips140_test.go

@@ -0,0 +1,48 @@
+package noiseutil
+
+import (
+	"crypto/cipher"
+	"crypto/fips140"
+	"encoding/hex"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Ensure NewAESGCM validates the nonce is non-repeating
+func TestNewAESGCM(t *testing.T) {
+	if !boringEnabled && !fips140.Enabled() {
+		t.Skip("TestNewAESGCM is only for fips140/boringcrypto")
+	}
+
+	key, _ := hex.DecodeString("feffe9928665731c6d6a8f9467308308feffe9928665731c6d6a8f9467308308")
+	iv, _ := hex.DecodeString("00000000facedbaddecaf888")
+	plaintext, _ := hex.DecodeString("d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39")
+	aad, _ := hex.DecodeString("feedfacedeadbeeffeedfacedeadbeefabaddad2")
+	expected, _ := hex.DecodeString("6a65c2edd45bd63c7e29f40e3d2ed8ba2b99f4c83135383d5676652f255059ceb24863ff10afb1089db701245da87fb88d3acd5f9dd0770cac220c3c04145caf25e190aeb775e7080401c628")
+
+	var keyArray [32]byte
+	copy(keyArray[:], key)
+	c := CipherAESGCM.Cipher(keyArray)
+	aead := c.(cipher.AEAD)
+
+	dst := aead.Seal([]byte{}, iv, plaintext, aad)
+	t.Logf("%x", dst)
+	assert.Equal(t, expected, dst)
+
+	// We expect this to fail since we are re-encrypting with a repeat IV
+	switch {
+	case boringEnabled:
+		assert.PanicsWithError(t, "boringcrypto: EVP_AEAD_CTX_seal failed", func() {
+			dst = aead.Seal([]byte{}, iv, plaintext, aad)
+		})
+	case fips140.Version() == "v1.0.0":
+		assert.PanicsWithValue(t, "crypto/cipher: counter decreased", func() {
+			dst = aead.Seal([]byte{}, iv, plaintext, aad)
+		})
+	default:
+		assert.PanicsWithValue(t, "crypto/cipher: counter decreased or remained the same", func() {
+			dst = aead.Seal([]byte{}, iv, plaintext, aad)
+		})
+	}
+}

noiseutil/fips140enforce.go

@@ -0,0 +1,13 @@
+//go:build fips140enforce
+
+package noiseutil
+
+import (
+	"crypto/fips140"
+)
+
+func init() {
+	if !fips140.Enforced() {
+		panic("Nebula compiled with fips140 expects FIPS140 to be enforced. Do not set GODEBUG=fips140, or if you do it must be set as GODEBUG=fips140=only")
+	}
+}

noiseutil/notboring.go

@@ -1,14 +1,25 @@
 //go:build !boringcrypto
-// +build !boringcrypto
 
 package noiseutil
 
 import (
+	"crypto/fips140"
+
 	"github.com/flynn/noise"
 )
 
 // EncryptLockNeeded indicates if calls to Encrypt need a lock
-const EncryptLockNeeded = false
+var EncryptLockNeeded = fips140.Enabled()
 
-// CipherAESGCM is the standard noise.CipherAESGCM when boringcrypto is not enabled
-var CipherAESGCM noise.CipherFunc = noise.CipherAESGCM
+var CipherAESGCM noise.CipherFunc = initAESGCM()
+
+func initAESGCM() noise.CipherFunc {
+	if fips140.Enabled() {
+		return CipherAESGCMFIPS140
+	} else {
+		return noise.CipherAESGCM
+	}
+
+}
+
+var boringEnabled = false

noiseutil/notboring_test.go

@@ -1,14 +0,0 @@
-//go:build !boringcrypto
-// +build !boringcrypto
-
-package noiseutil
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-)
-
-func TestEncryptLockNeeded(t *testing.T) {
-	assert.False(t, EncryptLockNeeded)
-}

outside.go

@@ -8,11 +8,12 @@ import (
 	"net/netip"
 	"time"
 
-	"github.com/google/gopacket/layers"
 	"golang.org/x/net/ipv6"
 
 	"github.com/slackhq/nebula/firewall"
 	"github.com/slackhq/nebula/header"
+	"github.com/slackhq/nebula/iputil"
+	"github.com/slackhq/nebula/overlay/batch"
 	"golang.org/x/net/ipv4"
 )
 
@@ -22,7 +23,11 @@ const (
 
 var ErrOutOfWindow = errors.New("out of window packet")
 
-func (f *Interface) readOutsidePackets(via ViaSender, out []byte, packet []byte, h *header.H, fwPacket *firewall.Packet, lhf *LightHouseHandler, nb []byte, q int, localCache firewall.ConntrackCache) {
+// readOutsidePackets processes one received underlay packet.
+// Message payloads are decrypted IN PLACE, so packet must stay untouched
+// by the caller until the batcher for queue q has been flushed
+func (f *Interface) readOutsidePackets(via ViaSender, packet []byte, rxc *rxContext) {
+	h := rxc.h
 	err := h.Parse(packet)
 	if err != nil {
 		// Hole punch packets are 0 or 1 byte big, so lets ignore printing those errors
@@ -90,52 +95,104 @@ func (f *Interface) readOutsidePackets(via ViaSender, out []byte, packet []byte,
 	if isMessageRelay {
 		hostinfo = f.hostMap.QueryRelayIndex(h.RemoteIndex)
 	} else {
-		hostinfo = f.hostMap.QueryIndex(h.RemoteIndex)
+		hostinfo = f.hostMap.QueryIndexCached(h.RemoteIndex, rxc.hostmapCache)
 	}
 
 	// At this point we should have a valid existing tunnel, verify and send
 	// recvError if necessary
 	if hostinfo == nil || hostinfo.ConnectionState == nil {
 		if !via.IsRelayed {
-			f.maybeSendRecvError(via.UdpAddr, h.RemoteIndex)
+			f.maybeSendRecvError(via.UdpAddr, h.RemoteIndex, via.SockIdx)
+		}
+		return
+	}
+
+	// Which session decrypts this packet is the lane index in the header. Lane 0
+	// is the base tunnel; a higher lane is one of the sessions derived from it.
+	ci := hostinfo.ConnectionState
+	lane := h.Lane()
+	laneCached := true
+	if lane != 0 {
+		if isMessageRelay {
+			// A relay carrier is always the base tunnel, so lane ciphertext can
+			// never legitimately arrive wrapped in one. Checked before the lookup
+			// below so a junk relay packet can't make us derive a session.
+			f.messageMetrics.RxInvalid(1)
+			if f.l.Enabled(context.Background(), slog.LevelDebug) {
+				hostinfo.logger(f.l).Debug("Refusing relayed multiport lane packet", "from", via, "header", h)
+			}
+			return
+		}
+
+		var err error
+		ci, laneCached, err = hostinfo.laneSession(lane)
+		if err != nil {
+			f.messageMetrics.RxInvalid(1)
+			hostinfo.logger(f.l).Error("Failed to derive multiport lane session", "error", err, "lane", lane)
+			return
+		}
+		if ci == nil {
+			// A lane this tunnel doesn't have: a stale lane from a tunnel that has
+			// since rolled, or a peer sending above what it advertised. Dropping
+			// silently is right for both — a recv_error would tear down a
+			// perfectly good base tunnel on the strength of one odd packet.
+			f.messageMetrics.RxInvalid(1)
+			if f.l.Enabled(context.Background(), slog.LevelDebug) {
+				hostinfo.logger(f.l).Debug("Unknown multiport lane", "from", via, "header", h)
+			}
+			return
+		}
+	}
+
+	if len(packet) < header.Len+ci.dKey.Overhead() {
+		f.messageMetrics.RxInvalid(1)
+		if f.l.Enabled(context.Background(), slog.LevelDebug) {
+			f.l.Debug("packet too small", "from", via, "length", len(packet))
 		}
 		return
 	}
 
 	// All remaining packets are encrypted
-	ci := hostinfo.ConnectionState
-	if !ci.window.Check(f.l, h.MessageCounter) {
-		return
-	}
-
-	// Relay packets are special
 	if isMessageRelay {
-		f.handleOutsideRelayPacket(hostinfo, via, out, packet, h, fwPacket, lhf, nb, q, localCache)
-
+		// Relay packets are special, this branch should always early-return
+		err = ci.VerifyRelay(f.l, h.MessageCounter, packet, rxc.nb)
+		if err != nil {
+			if f.l.Enabled(context.Background(), slog.LevelDebug) {
+				hostinfo.logger(f.l).Debug("Failed to verify relay packet", "error", err, "from", via, "header", h)
+			}
+			return
+		}
+		f.handleOutsideRelayPacket(hostinfo, via, packet, rxc)
 		return
 	}
 
-	out, err = f.decrypt(hostinfo, h.MessageCounter, out, packet, h, nb)
+	out, err := ci.Decrypt(f.l, h.MessageCounter, packet, rxc.nb)
 	if err != nil {
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
-			hostinfo.logger(f.l).Debug("Failed to decrypt packet",
-				"error", err,
-				"from", via,
-				"header", h,
-			)
+			hostinfo.logger(f.l).Debug("Failed to decrypt packet", "error", err, "from", via, "header", h)
 		}
 		return
 	}
 
-	// Roam before we respond
-	f.handleHostRoaming(hostinfo, via)
+	if !laneCached {
+		// The packet decrypted, so the peer really is using this lane and the
+		// session we derived for it is worth keeping.
+		hostinfo.lanes.installSession(f.l, lane, ci, h.MessageCounter)
+	}
+
+	// Roam before we respond, but only on the base tunnel: a lane's source
+	// address is a per-lane 4-tuple, not the tunnel's remote, and letting it
+	// roam the hostinfo would point every non-lane packet at a lane port.
+	if lane == 0 {
+		f.handleHostRoaming(hostinfo, via)
+	}
 	f.connectionManager.In(hostinfo)
 
 	switch h.Type {
 	case header.Message:
 		switch h.Subtype {
 		case header.MessageNone:
-			f.handleOutsideMessagePacket(hostinfo, out, packet, fwPacket, nb, q, localCache)
+			f.handleOutsideMessagePacket(hostinfo, ci, h.MessageCounter, out, rxc)
 		default:
 			hostinfo.logger(f.l).Error("IsValidSubType was true, but unexpected message subtype seen", "from", via, "header", h)
 			return
@@ -143,15 +200,27 @@ func (f *Interface) readOutsidePackets(via ViaSender, out []byte, packet []byte,
 
 	case header.LightHouse:
 		//TODO: assert via is not relayed
-		lhf.HandleRequest(via.UdpAddr, hostinfo.vpnAddrs, out, f)
+		rxc.lhh.HandleRequest(via.UdpAddr, hostinfo.vpnAddrs, out, f)
 
 	case header.Test:
 		switch h.Subtype {
 		case header.TestReply:
 			// No-op, useful for the Roaming and connectionManager side-effects above
 		case header.TestRequest:
-			//recycle the input packet ciphertext as our output buffer
-			f.send(header.Test, header.TestReply, ci, hostinfo, out, nb, packet)
+			const maxCipherOverhead = 16 //todo we use this too often, needs a real importable const
+			const maxOverhead = header.Len + header.Len + maxCipherOverhead + maxCipherOverhead
+			if maxOverhead+len(out) > len(rxc.scratch) {
+				// A reply that cannot fit in scratch is dropped no matter the log level.
+				if f.l.Enabled(context.Background(), slog.LevelDebug) {
+					hostinfo.logger(f.l).Debug("dropping oversized test request", "payloadLen", len(out), "from", via)
+				}
+				return
+			}
+			f.send(header.Test, header.TestReply, hostinfo.ConnectionState, hostinfo, out, rxc.nb, rxc.scratch[:0])
+		case header.LaneProbe:
+			f.handleLaneProbe(hostinfo, lane, out, rxc)
+		case header.LaneProbeAck:
+			f.handleLaneProbeAck(hostinfo, out)
 		default:
 			hostinfo.logger(f.l).Error("IsValidSubType was true, but unexpected test subtype seen", "from", via, "header", h)
 			return
@@ -169,28 +238,10 @@ func (f *Interface) readOutsidePackets(via ViaSender, out []byte, packet []byte,
 	}
 }
 
-func (f *Interface) handleOutsideRelayPacket(hostinfo *HostInfo, via ViaSender, out []byte, packet []byte, h *header.H, fwPacket *firewall.Packet, lhf *LightHouseHandler, nb []byte, q int, localCache firewall.ConntrackCache) {
-	// The entire body is sent as AD, not encrypted.
-	// The packet consists of a 16-byte parsed Nebula header, Associated Data-protected payload, and a trailing 16-byte AEAD signature value.
-	// The packet is guaranteed to be at least 16 bytes at this point, b/c it got past the h.Parse() call above. If it's
-	// otherwise malformed (meaning, there is no trailing 16 byte AEAD value), then this will result in at worst a 0-length slice
-	// which will gracefully fail in the DecryptDanger call.
-	signedPayload := packet[:len(packet)-hostinfo.ConnectionState.dKey.Overhead()]
-	signatureValue := packet[len(packet)-hostinfo.ConnectionState.dKey.Overhead():]
-	var err error
-	out, err = hostinfo.ConnectionState.dKey.DecryptDanger(out, signedPayload, signatureValue, h.MessageCounter, nb)
-	if err != nil {
-		return
-	}
-	// Advance the replay window now that the frame is authenticated
-	if !hostinfo.ConnectionState.window.Update(f.l, h.MessageCounter) {
-		if f.l.Enabled(context.Background(), slog.LevelDebug) {
-			hostinfo.logger(f.l).Debug("dropping out of window relay packet", "header", h)
-		}
-		return
-	}
-	// Successfully validated the thing. Get rid of the Relay header.
-	signedPayload = signedPayload[header.Len:]
+func (f *Interface) handleOutsideRelayPacket(hostinfo *HostInfo, via ViaSender, packet []byte, rxc *rxContext) {
+	h := rxc.h
+	// Successfully validated the thing. Get rid of the Relay header and the AEAD tag
+	signedPayload := packet[header.Len : len(packet)-hostinfo.ConnectionState.dKey.Overhead()]
 	// Pull the Roaming parts up here, and return in all call paths.
 	f.handleHostRoaming(hostinfo, via)
 	// Track usage of both the HostInfo and the Relay for the received & authenticated packet
@@ -201,9 +252,7 @@ func (f *Interface) handleOutsideRelayPacket(hostinfo *HostInfo, via ViaSender,
 	if !ok {
 		// The only way this happens is if hostmap has an index to the correct HostInfo, but the HostInfo is missing
 		// its internal mapping. This should never happen.
-		hostinfo.logger(f.l).Error("HostInfo missing remote relay index",
-			"relayRemoteIndex", h.RemoteIndex,
-		)
+		hostinfo.logger(f.l).Error("HostInfo missing remote relay index", "relayRemoteIndex", h.RemoteIndex)
 		return
 	}
 
@@ -214,11 +263,11 @@ func (f *Interface) handleOutsideRelayPacket(hostinfo *HostInfo, via ViaSender,
 		via = ViaSender{
 			UdpAddr:   via.UdpAddr,
 			relayHI:   hostinfo,
-			remoteIdx: relay.RemoteIndex,
 			relay:     relay,
 			IsRelayed: true,
+			SockIdx:   via.SockIdx,
 		}
-		f.readOutsidePackets(via, out[:0], signedPayload, h, fwPacket, lhf, nb, q, localCache)
+		f.readOutsidePackets(via, signedPayload, rxc)
 	case ForwardingType:
 		// Find the target HostInfo relay object
 		targetHI, targetRelay, err := f.hostMap.QueryVpnAddrsRelayFor(hostinfo.vpnAddrs, relay.PeerAddr)
@@ -235,9 +284,11 @@ func (f *Interface) handleOutsideRelayPacket(hostinfo *HostInfo, via ViaSender,
 		if targetRelay.State == Established {
 			switch targetRelay.Type {
 			case ForwardingType:
-				// Forward this packet through the relay tunnel
-				// Find the target HostInfo
-				f.SendVia(targetHI, targetRelay, signedPayload, nb, out, false)
+				// Forward this packet through the relay tunnel, rebuilding it in place.
+				// Encode overwrites the old outer header, and the new AEAD tag lands where the old one was
+				fwdBuf := packet[:0]
+				//todo it would potentially be nice to batch these
+				f.SendVia(targetHI, targetRelay, signedPayload, rxc.nb, fwdBuf, true, rxc.q)
 			case TerminalType:
 				hostinfo.logger(f.l).Error("Unexpected Relay Type of Terminal")
 				return
@@ -314,11 +365,14 @@ var (
 	ErrIPv4InvalidHeaderLength = errors.New("invalid ipv4 header length")
 	ErrIPv4PacketTooShort      = errors.New("ipv4 packet is too short")
 	ErrIPv6PacketTooShort      = errors.New("ipv6 packet is too short")
-	ErrIPv6CouldNotFindPayload = errors.New("could not find payload in ipv6 packet")
 )
 
 // newPacket validates and parses the interesting bits for the firewall out of the ip and sub protocol headers
-func newPacket(data []byte, incoming bool, fp *firewall.Packet) error {
+func newPacket(data []byte, incoming bool, fp *firewall.ParsedPacket) error {
+	// fp is reused across packets; reset the parse byproducts so an early-error return cannot
+	// leak the previous packet's offsets.
+	fp.IPHdrLen = 0
+	fp.FragAny = false
 	if len(data) < 1 {
 		return ErrPacketTooShort
 	}
@@ -333,7 +387,7 @@ func newPacket(data []byte, incoming bool, fp *firewall.Packet) error {
 	return ErrUnknownIPVersion
 }
 
-func parseV6(data []byte, incoming bool, fp *firewall.Packet) error {
+func parseV6(data []byte, incoming bool, fp *firewall.ParsedPacket) error {
 	dataLen := len(data)
 	if dataLen < ipv6.HeaderLen {
 		return ErrIPv6PacketTooShort
@@ -347,104 +401,64 @@ func parseV6(data []byte, incoming bool, fp *firewall.Packet) error {
 		fp.RemoteAddr, _ = netip.AddrFromSlice(data[24:40])
 	}
 
-	protoAt := 6             // NextHeader is at 6 bytes into the ipv6 header
-	offset := ipv6.HeaderLen // Start at the end of the ipv6 header
-	next := 0
-	for {
-		if protoAt >= dataLen {
-			break
+	// Walk the extension header chain to the upper layer protocol. iputil.IPv6FindUpperProtocol is the single
+	// source of truth for which headers are extension headers, so this stays in lockstep with the reject path
+	// and cannot drift into misreading an unknown protocol (SCTP, GRE, etc.) as a forged transport.
+	proto, offset, isFragment, anyFragment, err := iputil.IPv6FindUpperProtocol(data)
+	if err != nil {
+		return ErrIPv6PacketTooShort
+	}
+
+	fp.Protocol = proto
+	fp.Fragment = isFragment
+	fp.FragAny = anyFragment
+	fp.IPHdrLen = offset
+	if isFragment {
+		// Non-first fragments carry no transport header, so we have no ports to read
+		fp.RemotePort = 0
+		fp.LocalPort = 0
+		return nil
+	}
+
+	switch proto {
+	case iputil.IPProtocolICMPv6:
+		// An ICMPv6 message is at least type, code and checksum, 4 bytes. Only echo carries more than we read.
+		if dataLen < offset+4 {
+			return ErrIPv6PacketTooShort
 		}
-		proto := layers.IPProtocol(data[protoAt])
-
-		switch proto {
-		case layers.IPProtocolESP, layers.IPProtocolNoNextHeader:
-			fp.Protocol = uint8(proto)
-			fp.RemotePort = 0
-			fp.LocalPort = 0
-			fp.Fragment = false
-			return nil
-
-		case layers.IPProtocolICMPv6:
+		fp.LocalPort = 0      //incoming vs outgoing doesn't matter for icmpv6
+		switch data[offset] { //icmp type
+		case iputil.ICMPv6TypeEchoRequest, iputil.ICMPv6TypeEchoReply:
 			if dataLen < offset+6 {
 				return ErrIPv6PacketTooShort
 			}
-			fp.Protocol = uint8(proto)
-			fp.LocalPort = 0 //incoming vs outgoing doesn't matter for icmpv6
-			icmptype := data[offset+1]
-			switch icmptype {
-			case layers.ICMPv6TypeEchoRequest, layers.ICMPv6TypeEchoReply:
-				fp.RemotePort = binary.BigEndian.Uint16(data[offset+4 : offset+6]) //identifier
-			default:
-				fp.RemotePort = 0
-			}
-			fp.Fragment = false
-			return nil
-
-		case layers.IPProtocolTCP, layers.IPProtocolUDP:
-			if dataLen < offset+4 {
-				return ErrIPv6PacketTooShort
-			}
-
-			fp.Protocol = uint8(proto)
-			if incoming {
-				fp.RemotePort = binary.BigEndian.Uint16(data[offset : offset+2])
-				fp.LocalPort = binary.BigEndian.Uint16(data[offset+2 : offset+4])
-			} else {
-				fp.LocalPort = binary.BigEndian.Uint16(data[offset : offset+2])
-				fp.RemotePort = binary.BigEndian.Uint16(data[offset+2 : offset+4])
-			}
-
-			fp.Fragment = false
-			return nil
-
-		case layers.IPProtocolIPv6Fragment:
-			// Fragment header is 8 bytes, need at least offset+4 to read the offset field
-			if dataLen < offset+8 {
-				return ErrIPv6PacketTooShort
-			}
-
-			// Check if this is the first fragment
-			fragmentOffset := binary.BigEndian.Uint16(data[offset+2:offset+4]) &^ uint16(0x7) // Remove the reserved and M flag bits
-			if fragmentOffset != 0 {
-				// Non-first fragment, use what we have now and stop processing
-				fp.Protocol = data[offset]
-				fp.Fragment = true
-				fp.RemotePort = 0
-				fp.LocalPort = 0
-				return nil
-			}
-
-			// The next loop should be the transport layer since we are the first fragment
-			next = 8 // Fragment headers are always 8 bytes
-
-		case layers.IPProtocolAH:
-			// Auth headers, used by IPSec, have a different meaning for header length
-			if dataLen <= offset+1 {
-				break
-			}
-			next = (int(data[offset+1]) + 2) << 2
-
+			fp.RemotePort = binary.BigEndian.Uint16(data[offset+4 : offset+6]) //identifier
 		default:
-			// Normal ipv6 header length processing
-			if dataLen <= offset+1 {
-				break
-			}
-			next = (int(data[offset+1]) + 1) << 3
+			fp.RemotePort = 0
 		}
 
-		if next <= 0 {
-			// Safety check, each ipv6 header has to be at least 8 bytes
-			next = 8
+	case iputil.IPProtocolTCP, iputil.IPProtocolUDP:
+		if dataLen < offset+4 {
+			return ErrIPv6PacketTooShort
+		}
+		if incoming {
+			fp.RemotePort = binary.BigEndian.Uint16(data[offset : offset+2])
+			fp.LocalPort = binary.BigEndian.Uint16(data[offset+2 : offset+4])
+		} else {
+			fp.LocalPort = binary.BigEndian.Uint16(data[offset : offset+2])
+			fp.RemotePort = binary.BigEndian.Uint16(data[offset+2 : offset+4])
 		}
 
-		protoAt = offset
-		offset = offset + next
+	default:
+		// don't set ports for protocols Nebula doesn't inspect
+		fp.RemotePort = 0
+		fp.LocalPort = 0
 	}
 
-	return ErrIPv6CouldNotFindPayload
+	return nil
 }
 
-func parseV4(data []byte, incoming bool, fp *firewall.Packet) error {
+func parseV4(data []byte, incoming bool, fp *firewall.ParsedPacket) error {
 	// Do we at least have an ipv4 header worth of data?
 	if len(data) < ipv4.HeaderLen {
 		return ErrIPv4PacketTooShort
@@ -461,6 +475,10 @@ func parseV4(data []byte, incoming bool, fp *firewall.Packet) error {
 	// Check if this is the second or further fragment of a fragmented packet.
 	flagsfrags := binary.BigEndian.Uint16(data[6:8])
 	fp.Fragment = (flagsfrags & 0x1FFF) != 0
+	// Any fragmentation at all (MF or offset): first fragments have readable ports for the
+	// firewall but must never be coalesced.
+	fp.FragAny = (flagsfrags & 0x3fff) != 0
+	fp.IPHdrLen = ihl
 
 	// Firewall handles protocol checks
 	fp.Protocol = data[9]
@@ -468,7 +486,7 @@ func parseV4(data []byte, incoming bool, fp *firewall.Packet) error {
 	// Accounting for a variable header length, do we have enough data for our src/dst tuples?
 	minLen := ihl
 	if !fp.Fragment {
-		if fp.Protocol == firewall.ProtoICMP {
+		if fp.Protocol == iputil.IPProtocolICMP {
 			minLen += minFwPacketLen + 2
 		} else {
 			minLen += minFwPacketLen
@@ -490,7 +508,7 @@ func parseV4(data []byte, incoming bool, fp *firewall.Packet) error {
 	if fp.Fragment {
 		fp.RemotePort = 0
 		fp.LocalPort = 0
-	} else if fp.Protocol == firewall.ProtoICMP { //note that orientation doesn't matter on ICMP
+	} else if fp.Protocol == iputil.IPProtocolICMP { //note that orientation doesn't matter on ICMP
 		fp.RemotePort = binary.BigEndian.Uint16(data[ihl+4 : ihl+6]) //identifier
 		fp.LocalPort = 0                                             //code would be uint16(data[ihl+1])
 	} else if incoming {
@@ -504,61 +522,44 @@ func parseV4(data []byte, incoming bool, fp *firewall.Packet) error {
 	return nil
 }
 
-func (f *Interface) decrypt(hostinfo *HostInfo, mc uint64, out []byte, packet []byte, h *header.H, nb []byte) ([]byte, error) {
-	var err error
-	out, err = hostinfo.ConnectionState.dKey.DecryptDanger(out, packet[:header.Len], packet[header.Len:], mc, nb)
+func (f *Interface) handleOutsideMessagePacket(hostinfo *HostInfo, ci *ConnectionState, messageCounter uint64, out []byte, rxc *rxContext) {
+	err := newPacket(out, true, rxc.fwPacket)
 	if err != nil {
-		return nil, err
-	}
-
-	if !hostinfo.ConnectionState.window.Update(f.l, mc) {
-		return nil, ErrOutOfWindow
-	}
-
-	return out, nil
-}
-
-func (f *Interface) handleOutsideMessagePacket(hostinfo *HostInfo, out []byte, packet []byte, fwPacket *firewall.Packet, nb []byte, q int, localCache firewall.ConntrackCache) {
-	err := newPacket(out, true, fwPacket)
-	if err != nil {
-		hostinfo.logger(f.l).Warn("Error while validating inbound packet",
-			"error", err,
-			"packet", out,
-		)
+		hostinfo.logger(f.l).Warn("Error while validating inbound packet", "error", err, "packet", out)
 		return
 	}
 
-	dropReason := f.firewall.Drop(*fwPacket, true, hostinfo, f.pki.GetCAPool(), localCache)
+	dropReason := f.firewall.Drop(rxc.fwPacket.Packet, true, hostinfo, f.pki.GetCAPool(), rxc.ctCache.Get())
 	if dropReason != nil {
-		// NOTE: We give `packet` as the `out` here since we already decrypted from it and we don't need it anymore
-		// This gives us a buffer to build the reject packet in
-		f.rejectOutside(out, hostinfo.ConnectionState, hostinfo, nb, packet, q)
+		// The reject rides the base tunnel: it is a control response, not lane
+		// data, and the lane it arrived on says nothing about where it belongs.
+		f.rejectOutside(out, hostinfo.ConnectionState, hostinfo, rxc.nb, rxc.scratch, rxc.q)
 		if f.l.Enabled(context.Background(), slog.LevelDebug) {
-			hostinfo.logger(f.l).Debug("dropping inbound packet",
-				"fwPacket", fwPacket,
-				"reason", dropReason,
-			)
+			hostinfo.logger(f.l).Debug("dropping inbound packet", "fwPacket", rxc.fwPacket, "reason", dropReason)
 		}
 		return
 	}
 
-	_, err = f.readers[q].Write(out)
+	err = f.batchers[rxc.q].Commit(out, batch.SortKey{Epoch: ci.epoch, Counter: messageCounter}, rxc.fwPacket)
 	if err != nil {
 		f.l.Error("Failed to write to tun", "error", err)
 	}
 }
 
-func (f *Interface) maybeSendRecvError(endpoint netip.AddrPort, index uint32) {
+func (f *Interface) maybeSendRecvError(endpoint netip.AddrPort, index uint32, q int) {
 	if f.sendRecvErrorConfig.ShouldRecvError(endpoint) {
-		f.sendRecvError(endpoint, index)
+		f.sendRecvError(endpoint, index, q)
 	}
 }
 
-func (f *Interface) sendRecvError(endpoint netip.AddrPort, index uint32) {
+// sendRecvError replies from the socket the offending packet arrived on (q).
+// A lane peer's spoof guard compares our source addr against the lane's
+// remote, so a reply from the base port would be discarded.
+func (f *Interface) sendRecvError(endpoint netip.AddrPort, index uint32, q int) {
 	f.messageMetrics.Tx(header.RecvError, 0, 1)
 
 	b := header.Encode(make([]byte, header.Len), header.Version, header.RecvError, 0, index, 0)
-	_ = f.outside.WriteTo(b, endpoint)
+	_ = f.writers[q].WriteTo(b, endpoint)
 	if f.l.Enabled(context.Background(), slog.LevelDebug) {
 		f.l.Debug("Recv error sent",
 			"index", index,

outside_test.go

@@ -9,15 +9,17 @@ import (
 
 	"github.com/google/gopacket"
 	"github.com/google/gopacket/layers"
+	"github.com/slackhq/nebula/iputil"
 
 	"github.com/slackhq/nebula/firewall"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
 )
 
 func Test_newPacket(t *testing.T) {
-	p := &firewall.Packet{}
+	p := &firewall.ParsedPacket{}
 
 	// length fails
 	err := newPacket([]byte{}, true, p)
@@ -57,7 +59,7 @@ func Test_newPacket(t *testing.T) {
 		Src:      net.IPv4(10, 0, 0, 1),
 		Dst:      net.IPv4(10, 0, 0, 2),
 		Options:  []byte{0, 1, 0, 2},
-		Protocol: firewall.ProtoTCP,
+		Protocol: iputil.IPProtocolTCP,
 	}
 
 	b, _ = h.Marshal()
@@ -65,7 +67,7 @@ func Test_newPacket(t *testing.T) {
 	err = newPacket(b, true, p)
 
 	require.NoError(t, err)
-	assert.Equal(t, uint8(firewall.ProtoTCP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolTCP), p.Protocol)
 	assert.Equal(t, netip.MustParseAddr("10.0.0.2"), p.LocalAddr)
 	assert.Equal(t, netip.MustParseAddr("10.0.0.1"), p.RemoteAddr)
 	assert.Equal(t, uint16(3), p.RemotePort)
@@ -96,7 +98,7 @@ func Test_newPacket(t *testing.T) {
 }
 
 func Test_newPacket_v6(t *testing.T) {
-	p := &firewall.Packet{}
+	p := &firewall.ParsedPacket{}
 
 	// invalid ipv6
 	ip := layers.IPv6{
@@ -115,12 +117,12 @@ func Test_newPacket_v6(t *testing.T) {
 	require.NoError(t, err)
 
 	err = newPacket(buffer.Bytes(), true, p)
-	require.ErrorIs(t, err, ErrIPv6CouldNotFindPayload)
+	require.ErrorIs(t, err, ErrIPv6PacketTooShort)
 
 	// A v6 packet with a hop-by-hop extension
 	// ICMPv6 Payload (Echo Request)
 	icmpLayer := layers.ICMPv6{
-		TypeCode: layers.ICMPv6TypeEchoRequest,
+		TypeCode: layers.CreateICMPv6TypeCode(layers.ICMPv6TypeEchoRequest, 0),
 	}
 	// Hop-by-Hop Extension Header
 	hopOption := layers.IPv6HopByHopOption{}
@@ -149,12 +151,12 @@ func Test_newPacket_v6(t *testing.T) {
 	// A full IPv6 header and 1 byte in the first extension, but missing
 	// the length byte.
 	err = newPacket(buffer.Bytes()[:41], true, p)
-	require.ErrorIs(t, err, ErrIPv6CouldNotFindPayload)
+	require.ErrorIs(t, err, ErrIPv6PacketTooShort)
 
 	// A full IPv6 header plus 1 full extension, but only 1 byte of the
 	// next layer, missing length byte
 	err = newPacket(buffer.Bytes()[:49], true, p)
-	require.ErrorIs(t, err, ErrIPv6CouldNotFindPayload)
+	require.ErrorIs(t, err, ErrIPv6PacketTooShort)
 	err = nil
 
 	// A good ICMP packet
@@ -167,7 +169,7 @@ func Test_newPacket_v6(t *testing.T) {
 	}
 
 	icmp := layers.ICMPv6{
-		TypeCode: layers.ICMPv6TypeEchoRequest,
+		TypeCode: layers.CreateICMPv6TypeCode(layers.ICMPv6TypeEchoRequest, 0),
 		Checksum: 0x1234,
 	}
 
@@ -189,6 +191,18 @@ func Test_newPacket_v6(t *testing.T) {
 	assert.Equal(t, uint16(0), p.LocalPort)
 	assert.False(t, p.Fragment)
 
+	// A minimal 4 byte non-echo ICMPv6 message (type, code, checksum), no identifier to read
+	icmpMin := make([]byte, ipv6.HeaderLen+4)
+	copy(icmpMin, buffer.Bytes()[:ipv6.HeaderLen])
+	icmpMin[6] = byte(layers.IPProtocolICMPv6)
+	icmpMin[ipv6.HeaderLen] = 1 // type 1, destination unreachable, not echo
+	err = newPacket(icmpMin, true, p)
+	require.NoError(t, err)
+	assert.Equal(t, uint8(layers.IPProtocolICMPv6), p.Protocol)
+	assert.Equal(t, uint16(0), p.RemotePort)
+	assert.Equal(t, uint16(0), p.LocalPort)
+	assert.False(t, p.Fragment)
+
 	// A good ESP packet
 	b := buffer.Bytes()
 	b[6] = byte(layers.IPProtocolESP)
@@ -213,16 +227,20 @@ func Test_newPacket_v6(t *testing.T) {
 	assert.Equal(t, uint16(0), p.LocalPort)
 	assert.False(t, p.Fragment)
 
-	// An unknown protocol packet
+	// An unknown protocol packet, we don't dissect it so we fail closed on its true protocol with no ports
 	b = buffer.Bytes()
 	b[6] = 255 // 255 is a reserved protocol number
 	err = newPacket(b, true, p)
-	require.ErrorIs(t, err, ErrIPv6CouldNotFindPayload)
+	require.NoError(t, err)
+	assert.Equal(t, uint8(255), p.Protocol)
+	assert.Equal(t, uint16(0), p.RemotePort)
+	assert.Equal(t, uint16(0), p.LocalPort)
+	assert.False(t, p.Fragment)
 
 	// A good UDP packet
 	ip = layers.IPv6{
 		Version:    6,
-		NextHeader: firewall.ProtoUDP,
+		NextHeader: iputil.IPProtocolUDP,
 		HopLimit:   128,
 		SrcIP:      net.IPv6linklocalallrouters,
 		DstIP:      net.IPv6linklocalallnodes,
@@ -245,7 +263,7 @@ func Test_newPacket_v6(t *testing.T) {
 	// incoming
 	err = newPacket(b, true, p)
 	require.NoError(t, err)
-	assert.Equal(t, uint8(firewall.ProtoUDP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolUDP), p.Protocol)
 	assert.Equal(t, netip.MustParseAddr("ff02::2"), p.RemoteAddr)
 	assert.Equal(t, netip.MustParseAddr("ff02::1"), p.LocalAddr)
 	assert.Equal(t, uint16(36123), p.RemotePort)
@@ -255,7 +273,7 @@ func Test_newPacket_v6(t *testing.T) {
 	// outgoing
 	err = newPacket(b, false, p)
 	require.NoError(t, err)
-	assert.Equal(t, uint8(firewall.ProtoUDP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolUDP), p.Protocol)
 	assert.Equal(t, netip.MustParseAddr("ff02::2"), p.LocalAddr)
 	assert.Equal(t, netip.MustParseAddr("ff02::1"), p.RemoteAddr)
 	assert.Equal(t, uint16(36123), p.LocalPort)
@@ -272,7 +290,7 @@ func Test_newPacket_v6(t *testing.T) {
 	// incoming
 	err = newPacket(b, true, p)
 	require.NoError(t, err)
-	assert.Equal(t, uint8(firewall.ProtoTCP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolTCP), p.Protocol)
 	assert.Equal(t, netip.MustParseAddr("ff02::2"), p.RemoteAddr)
 	assert.Equal(t, netip.MustParseAddr("ff02::1"), p.LocalAddr)
 	assert.Equal(t, uint16(36123), p.RemotePort)
@@ -282,7 +300,7 @@ func Test_newPacket_v6(t *testing.T) {
 	// outgoing
 	err = newPacket(b, false, p)
 	require.NoError(t, err)
-	assert.Equal(t, uint8(firewall.ProtoTCP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolTCP), p.Protocol)
 	assert.Equal(t, netip.MustParseAddr("ff02::2"), p.LocalAddr)
 	assert.Equal(t, netip.MustParseAddr("ff02::1"), p.RemoteAddr)
 	assert.Equal(t, uint16(36123), p.LocalPort)
@@ -327,25 +345,25 @@ func Test_newPacket_v6(t *testing.T) {
 
 	err = newPacket(b, true, p)
 	require.NoError(t, err)
-	assert.Equal(t, uint8(firewall.ProtoUDP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolUDP), p.Protocol)
 	assert.Equal(t, netip.MustParseAddr("ff02::2"), p.RemoteAddr)
 	assert.Equal(t, netip.MustParseAddr("ff02::1"), p.LocalAddr)
 	assert.Equal(t, uint16(36123), p.RemotePort)
 	assert.Equal(t, uint16(22), p.LocalPort)
 	assert.False(t, p.Fragment)
 
-	// Ensure buffer bounds checking during processing
+	// Ensure buffer bounds checking during processing, a truncated AH header can't reach the payload
 	err = newPacket(b[:41], true, p)
 	require.ErrorIs(t, err, ErrIPv6PacketTooShort)
 
 	// Invalid AH header
 	b = buffer.Bytes()
 	err = newPacket(b, true, p)
-	require.ErrorIs(t, err, ErrIPv6CouldNotFindPayload)
+	require.ErrorIs(t, err, ErrIPv6PacketTooShort)
 }
 
 func Test_newPacket_ipv6Fragment(t *testing.T) {
-	p := &firewall.Packet{}
+	p := &firewall.ParsedPacket{}
 
 	ip := &layers.IPv6{
 		Version:    6,
@@ -525,7 +543,7 @@ func BenchmarkParseV6(b *testing.B) {
 	secondFrag = append(secondFrag, fragHeader...)
 	secondFrag = append(secondFrag, []byte{0xde, 0xad, 0xbe, 0xef}...)
 
-	fp := &firewall.Packet{}
+	fp := &firewall.ParsedPacket{}
 
 	b.Run("Normal", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
@@ -649,7 +667,7 @@ func serializeAH(ah *layers.IPSecAH) []byte {
 // host OS parses the real header, a firewall port/proto bypass. The fix makes parseV6 land
 // on the same offset the host does.
 func Test_newPacket_v6ExtHeaderOverflow(t *testing.T) {
-	p := &firewall.Packet{}
+	p := &firewall.ParsedPacket{}
 
 	const (
 		hdrLen      = 40              // IPv6 header
@@ -661,7 +679,7 @@ func Test_newPacket_v6ExtHeaderOverflow(t *testing.T) {
 	pkt := make([]byte, realTCPAt+4)
 	pkt[0] = 0x60                                   // version 6
 	pkt[6] = byte(layers.IPProtocolIPv6Destination) // NextHeader -> Destination Options
-	pkt[40] = byte(firewall.ProtoTCP)               // Dest-Options NextHeader -> TCP
+	pkt[40] = byte(iputil.IPProtocolTCP)            // Dest-Options NextHeader -> TCP
 	pkt[41] = 255                                   // HdrExtLen = 255
 
 	// Forged transport header at the pre-fix (wrong) offset: dst port 443.
@@ -670,8 +688,156 @@ func Test_newPacket_v6ExtHeaderOverflow(t *testing.T) {
 	binary.BigEndian.PutUint16(pkt[realTCPAt+2:realTCPAt+4], 22)
 
 	require.NoError(t, newPacket(pkt, true, p))
-	assert.Equal(t, uint8(firewall.ProtoTCP), p.Protocol)
+	assert.Equal(t, uint8(iputil.IPProtocolTCP), p.Protocol)
 	// LocalPort is the destination port for incoming traffic. It must be the real port (22)
 	// the host delivers to, not the forged 443 at the overflowed offset.
 	assert.Equal(t, uint16(22), p.LocalPort, "firewall must parse the real transport header, not the overflowed offset")
 }
+
+// Test_newPacket_v6ExtHeaderPastBuffer is a regression test for an extension header whose declared length
+// advances the walk past the end of the packet. The upper layer protocol's header isn't actually present,
+// so parseV6 must drop the packet rather than classify it as the terminal protocol with no ports.
+func Test_newPacket_v6ExtHeaderPastBuffer(t *testing.T) {
+	p := &firewall.ParsedPacket{}
+
+	pkt := make([]byte, 48)
+	pkt[0] = 0x60
+	pkt[6] = byte(layers.IPProtocolIPv6Destination) // Destination Options
+	pkt[7] = 64                                     // hop limit
+	pkt[40] = byte(layers.IPProtocolSCTP)           // Dest Options next header = SCTP
+	pkt[41] = 255                                   // declared length (255+1)*8 = 2048, past the 48 byte buffer
+
+	require.ErrorIs(t, newPacket(pkt, true, p), ErrIPv6PacketTooShort)
+}
+
+// Test_newPacket_v6ExtHeaderConfusion is a regression test for parseV6 walking any unrecognized
+// Next Header as if it were an ipv6 extension header. A real upper layer protocol Nebula doesn't
+// dissect (SCTP here) is not walkable, so applying the (len+1)*8 formula marched into the SCTP
+// payload and landed on a byte that looked like UDP, forging a protocol/port pair the firewall
+// would trust while the host delivered the real SCTP datagram. The fix fails closed: the packet
+// is classified as its true protocol with no ports, so it only matches an `any` rule.
+func Test_newPacket_v6ExtHeaderConfusion(t *testing.T) {
+	p := &firewall.ParsedPacket{}
+
+	pkt := make([]byte, 52)
+	pkt[0] = 0x60                        // version 6
+	pkt[6] = byte(layers.IPProtocolSCTP) // NextHeader = SCTP, a real protocol, not an extension header
+	pkt[7] = 64                          // hop limit
+
+	// Real SCTP header at offset 40. Pre-fix parseV6 walked SCTP as an extension header: byte 41 (0x00, the
+	// low byte of the src port below) was read as the header length, giving next=(0+1)*8=8, which landed the
+	// walk on byte 40 (0x11), misread as NextHeader=UDP, then bytes 48-51 as ports.
+	binary.BigEndian.PutUint16(pkt[40:42], 0x1100) // SCTP src port; byte 40=0x11, byte 41=0x00
+	binary.BigEndian.PutUint16(pkt[42:44], 445)    // SCTP dst port, never read by parseV6
+	binary.BigEndian.PutUint16(pkt[48:50], 53)     // SCTP checksum bytes, pre-fix forged RemotePort
+	binary.BigEndian.PutUint16(pkt[50:52], 53)     // pre-fix forged LocalPort
+
+	require.NoError(t, newPacket(pkt, true, p))
+	assert.Equal(t, uint8(layers.IPProtocolSCTP), p.Protocol, "must classify as the true protocol, not the forged UDP")
+	assert.Equal(t, uint16(0), p.RemotePort)
+	assert.Equal(t, uint16(0), p.LocalPort)
+	assert.False(t, p.Fragment)
+
+	// Same confusion, but the unknown protocol sits after a real extension header. The HopByHop is walked
+	// correctly, then SCTP must still fail closed instead of being walked into its own payload. Protocol is
+	// the only assertion that discriminates the fix here, a regression that walked SCTP would misclassify it.
+	chained := make([]byte, 60)
+	chained[0] = 0x60                                  // version 6
+	chained[6] = byte(layers.IPProtocolIPv6HopByHop)   // NextHeader = HopByHop extension
+	chained[7] = 64                                    // hop limit
+	chained[40] = byte(layers.IPProtocolSCTP)          // HopByHop NextHeader = SCTP
+	chained[41] = 0                                    // HopByHop length 0 -> 8 bytes, SCTP begins at offset 48
+	binary.BigEndian.PutUint16(chained[48:50], 0x1100) // SCTP src port, pre-fix forged NextHeader/length bait
+	binary.BigEndian.PutUint16(chained[50:52], 445)    // SCTP dst port, never read by parseV6
+
+	require.NoError(t, newPacket(chained, true, p))
+	assert.Equal(t, uint8(layers.IPProtocolSCTP), p.Protocol, "must fail closed on the unknown protocol after the extension header")
+	assert.Equal(t, uint16(0), p.RemotePort)
+	assert.Equal(t, uint16(0), p.LocalPort)
+	assert.False(t, p.Fragment)
+}
+
+// Test_newPacket_parsedFields pins the ParsedPacket byproducts the RX
+// batcher consumes: IPHdrLen (the true L4 offset) and FragAny (any fragment
+// shape at all — unlike Packet.Fragment, which is port-oriented and true
+// only for non-first fragments).
+func Test_newPacket_parsedFields(t *testing.T) {
+	p := &firewall.ParsedPacket{}
+
+	// Plain IPv4 TCP, IHL 20: L4 offset 20, no fragment shape.
+	v4 := make([]byte, 28)
+	v4[0] = 0x45
+	v4[9] = iputil.IPProtocolTCP
+	binary.BigEndian.PutUint16(v4[6:8], 0x4000) // DF only
+	require.NoError(t, newPacket(v4, true, p))
+	assert.Equal(t, 20, p.IPHdrLen)
+	assert.False(t, p.FragAny)
+	assert.False(t, p.Fragment)
+
+	// IPv4 first fragment (MF set, offset 0): the firewall can read ports
+	// (Fragment false) but the coalescer must not touch it (FragAny true).
+	ff := make([]byte, 28)
+	ff[0] = 0x45
+	ff[9] = iputil.IPProtocolUDP
+	binary.BigEndian.PutUint16(ff[6:8], 0x2000) // MF, offset 0
+	require.NoError(t, newPacket(ff, true, p))
+	assert.False(t, p.Fragment)
+	assert.True(t, p.FragAny)
+	assert.Equal(t, 20, p.IPHdrLen)
+
+	// IPv4 non-first fragment (nonzero offset): both flags set.
+	nf := make([]byte, 28)
+	nf[0] = 0x45
+	nf[9] = iputil.IPProtocolUDP
+	binary.BigEndian.PutUint16(nf[6:8], 0x00b9)
+	require.NoError(t, newPacket(nf, true, p))
+	assert.True(t, p.Fragment)
+	assert.True(t, p.FragAny)
+
+	// IPv4 with options (IHL 24): IPHdrLen tracks the real L4 offset.
+	opts := make([]byte, 32)
+	opts[0] = 0x46
+	opts[9] = iputil.IPProtocolTCP
+	binary.BigEndian.PutUint16(opts[6:8], 0x4000)
+	require.NoError(t, newPacket(opts, true, p))
+	assert.Equal(t, 24, p.IPHdrLen)
+	assert.False(t, p.FragAny)
+
+	// Plain IPv6 TCP: L4 at 40.
+	v6 := make([]byte, 60)
+	v6[0] = 0x60
+	v6[6] = iputil.IPProtocolTCP
+	require.NoError(t, newPacket(v6, true, p))
+	assert.Equal(t, 40, p.IPHdrLen)
+	assert.False(t, p.FragAny)
+
+	// IPv6 hop-by-hop then TCP: IPHdrLen lands past the extension header.
+	hbh := make([]byte, 60)
+	hbh[0] = 0x60
+	hbh[6] = 0 // hop-by-hop
+	hbh[40] = iputil.IPProtocolTCP
+	hbh[41] = 0 // HdrExtLen 0 -> 8-byte header
+	require.NoError(t, newPacket(hbh, true, p))
+	assert.Equal(t, 48, p.IPHdrLen)
+	assert.False(t, p.FragAny)
+
+	// IPv6 first fragment: terminal proto resolved, FragAny set, Fragment not.
+	f6 := make([]byte, 60)
+	f6[0] = 0x60
+	f6[6] = 44 // fragment extension header
+	f6[40] = iputil.IPProtocolUDP
+	require.NoError(t, newPacket(f6, true, p))
+	assert.True(t, p.FragAny)
+	assert.False(t, p.Fragment)
+	assert.Equal(t, uint8(iputil.IPProtocolUDP), p.Protocol)
+
+	// IPv6 non-first fragment: both set, walk stops at the fragment header.
+	f6n := make([]byte, 60)
+	f6n[0] = 0x60
+	f6n[6] = 44
+	f6n[40] = iputil.IPProtocolUDP
+	binary.BigEndian.PutUint16(f6n[42:44], 0x0008)
+	require.NoError(t, newPacket(f6n, true, p))
+	assert.True(t, p.Fragment)
+	assert.True(t, p.FragAny)
+}

overlay/batch/checksum_seed_test.go

@@ -0,0 +1,187 @@
+package batch
+
+import (
+	"encoding/binary"
+	"math/rand"
+	"testing"
+)
+
+// The checksum-seeding helpers feed the virtio NEEDS_CSUM contract: the L4
+// checksum field is pre-loaded with the folded (not inverted) pseudo-header
+// sum, and the kernel later adds the L4 byte sum and inverts. A wrong seed
+// produces packets every receiver silently drops, with nothing failing on
+// our side — so these tests check the helpers against an independent
+// RFC 1071 reference built from explicit pseudo-header bytes, never against
+// the production checksum code.
+
+// refSum accumulates big-endian 16-bit words of b (odd tail zero-padded)
+// into a wide one's-complement accumulator.
+func refSum(b []byte) uint64 {
+	var s uint64
+	for i := 0; i+1 < len(b); i += 2 {
+		s += uint64(b[i])<<8 | uint64(b[i+1])
+	}
+	if len(b)%2 == 1 {
+		s += uint64(b[len(b)-1]) << 8
+	}
+	return s
+}
+
+// refFold folds a wide one's-complement accumulator to 16 bits.
+func refFold(s uint64) uint16 {
+	for s>>16 != 0 {
+		s = s&0xffff + s>>16
+	}
+	return uint16(s)
+}
+
+func TestFoldOnceNoInvertEdgeCases(t *testing.T) {
+	cases := []uint32{
+		0, 1, 0xffff,
+		0x10000,    // single carry
+		0x1fffe,    // 0xffff + 0xffff: carry produces another 0xffff
+		0xffff0000, // high half only
+		0xfffeffff, // fold yields 0x1fffd: needs a second fold
+		0xffffffff, // worst case
+		0x00010001, // simple two-word
+	}
+	for _, c := range cases {
+		want := refFold(uint64(c))
+		if got := foldOnceNoInvert(c); got != want {
+			t.Errorf("foldOnceNoInvert(%#x) = %#x, want %#x", c, got, want)
+		}
+		// Folding a folded value must be a no-op.
+		if got := foldOnceNoInvert(uint32(foldOnceNoInvert(c))); got != foldOnceNoInvert(c) {
+			t.Errorf("foldOnceNoInvert not idempotent at %#x", c)
+		}
+	}
+}
+
+func TestPseudoSumIPv4MatchesReference(t *testing.T) {
+	cases := []struct {
+		name     string
+		src, dst [4]byte
+		proto    byte
+		l4Len    int
+	}{
+		{"simple", [4]byte{10, 0, 0, 1}, [4]byte{10, 0, 0, 2}, 6, 20},
+		{"zero-len", [4]byte{192, 168, 1, 1}, [4]byte{192, 168, 1, 2}, 17, 0},
+		{"max-len", [4]byte{1, 2, 3, 4}, [4]byte{5, 6, 7, 8}, 6, 65535},
+		{"carry-heavy", [4]byte{255, 255, 255, 255}, [4]byte{255, 255, 255, 254}, 17, 65535},
+		{"broadcastish", [4]byte{255, 255, 255, 255}, [4]byte{255, 255, 255, 255}, 255, 65535},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			// RFC 793 pseudo-header: src(4) dst(4) zero(1) proto(1) len(2).
+			ph := make([]byte, 12)
+			copy(ph[0:4], c.src[:])
+			copy(ph[4:8], c.dst[:])
+			ph[9] = c.proto
+			binary.BigEndian.PutUint16(ph[10:12], uint16(c.l4Len))
+			want := refFold(refSum(ph))
+
+			got := foldOnceNoInvert(pseudoSumIPv4(c.src[:], c.dst[:], c.proto, c.l4Len))
+			if got != want {
+				t.Errorf("fold(pseudoSumIPv4) = %#x, want %#x", got, want)
+			}
+		})
+	}
+}
+
+func TestPseudoSumIPv6MatchesReference(t *testing.T) {
+	ones := func(b byte) (a [16]byte) {
+		for i := range a {
+			a[i] = b
+		}
+		return
+	}
+	cases := []struct {
+		name     string
+		src, dst [16]byte
+		proto    byte
+		l4Len    int
+	}{
+		{"simple", [16]byte{0xfe, 0x80, 15: 1}, [16]byte{0xfe, 0x80, 15: 2}, 6, 20},
+		{"zero-len", [16]byte{0x20, 0x01, 15: 9}, [16]byte{0x20, 0x01, 15: 8}, 17, 0},
+		{"max-u16-len", ones(0xff), ones(0xfe), 6, 65535},
+		{"len-past-u16", ones(0xff), ones(0xff), 17, 0x12345}, // exercises the 32-bit split
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			// RFC 8200 pseudo-header: src(16) dst(16) len(4) zero(3) next(1).
+			ph := make([]byte, 40)
+			copy(ph[0:16], c.src[:])
+			copy(ph[16:32], c.dst[:])
+			binary.BigEndian.PutUint32(ph[32:36], uint32(c.l4Len))
+			ph[39] = c.proto
+			want := refFold(refSum(ph))
+
+			got := foldOnceNoInvert(pseudoSumIPv6(c.src[:], c.dst[:], c.proto, c.l4Len))
+			if got != want {
+				t.Errorf("fold(pseudoSumIPv6) = %#x, want %#x", got, want)
+			}
+		})
+	}
+}
+
+func TestIPv4HdrChecksumMatchesReference(t *testing.T) {
+	rng := rand.New(rand.NewSource(0x1791))
+	for _, hdrLen := range []int{20, 24, 40, 60} {
+		for trial := 0; trial < 200; trial++ {
+			hdr := make([]byte, hdrLen)
+			rng.Read(hdr)
+			hdr[0] = 0x40 | byte(hdrLen/4)
+			hdr[10], hdr[11] = 0, 0 // checksum field zeroed, as the contract requires
+
+			want := ^refFold(refSum(hdr))
+			got := ipv4HdrChecksum(hdr)
+			if got != want {
+				t.Fatalf("ipv4HdrChecksum(len=%d trial=%d) = %#x, want %#x", hdrLen, trial, got, want)
+			}
+
+			// Receiver-side property: with the checksum stored, the full
+			// header must sum to all-ones.
+			binary.BigEndian.PutUint16(hdr[10:12], got)
+			if v := refFold(refSum(hdr)); v != 0xffff {
+				t.Fatalf("stored checksum does not validate: full-header fold = %#x", v)
+			}
+		}
+	}
+}
+
+// TestChecksumSeedReceiverAcceptance is the end-to-end property the helpers
+// exist for: seed the TCP checksum field with fold(pseudoSum), do what the
+// kernel's NEEDS_CSUM completion does (one's-complement sum over the L4
+// bytes including the seed, then invert, then store), and verify the result
+// the way a receiver does (pseudo-header + L4 must sum to all-ones).
+func TestChecksumSeedReceiverAcceptance(t *testing.T) {
+	rng := rand.New(rand.NewSource(0x1826))
+	for trial := 0; trial < 200; trial++ {
+		src := [4]byte{byte(rng.Intn(256)), byte(rng.Intn(256)), byte(rng.Intn(256)), byte(rng.Intn(256))}
+		dst := [4]byte{byte(rng.Intn(256)), byte(rng.Intn(256)), byte(rng.Intn(256)), byte(rng.Intn(256))}
+		payLen := rng.Intn(1500)
+		l4 := make([]byte, 20+payLen)
+		rng.Read(l4)
+
+		// Seed exactly as flushSlot does.
+		seed := foldOnceNoInvert(pseudoSumIPv4(src[:], dst[:], 6, len(l4)))
+		binary.BigEndian.PutUint16(l4[16:18], seed)
+
+		// Kernel NEEDS_CSUM completion: sum the L4 region (seed included,
+		// which is equivalent to summing with the field zeroed and folding
+		// the seed in), invert, store.
+		final := ^refFold(refSum(l4[:16]) + uint64(seed) + refSum(l4[18:]))
+		binary.BigEndian.PutUint16(l4[16:18], final)
+
+		// Receiver validation.
+		ph := make([]byte, 12)
+		copy(ph[0:4], src[:])
+		copy(ph[4:8], dst[:])
+		ph[9] = 6
+		binary.BigEndian.PutUint16(ph[10:12], uint16(len(l4)))
+		if v := refFold(refSum(ph) + refSum(l4)); v != 0xffff {
+			t.Fatalf("trial %d: receiver rejects packet: fold = %#x (seed=%#x final=%#x payLen=%d)",
+				trial, v, seed, final, payLen)
+		}
+	}
+}

overlay/batch/coalesce_core.go

@@ -0,0 +1,169 @@
+package batch
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+// SortKey identifies a packet's position in its sender's transmission order.
+type SortKey struct {
+	// Epoch is a receiver-local ordinal for the tunnel (ConnectionState) that decrypted the packet:
+	// a re-handshake replaces the tunnel outright and the replacement's epoch is higher,
+	// so the old tunnel's packets sort first during the cutover overlap.
+	Epoch uint64
+	// Counter is the packet's AEAD message counter within that tunnel.
+	Counter uint64
+}
+
+// flowKey identifies a transport flow by {src, dst, sport, dport, family}.
+// Comparable, so map lookups and linear scans over the slot list stay tight.
+// Shared by the TCP and UDP coalescers; each coalescer keeps its own
+// openSlots map, so a TCP and UDP flow on the same 5-tuple-without-proto never alias.
+type flowKey struct {
+	src, dst     [16]byte
+	sport, dport uint16
+	isV6         bool
+}
+
+// initialSlots is the starting capacity of the slot pool.
+// One flow per packet is the worst case, so this matches a typical carrier-side recvmmsg batch on the UDP socket.
+const initialSlots = 64
+
+// parseIPAt validates the IP header for lane parsing. newPacket already resolved the L4 protocol
+// and offset for the firewall, so there is no proto sniff here; the caller's ipHdrLen is
+// cross-checked instead. A plain header (v4 IHL 20, v6 exactly 40) is the only coalesceable
+// shape. The v6 check is load-bearing: it rejects extension-header packets whose L4 is not at byte 40.
+//
+// The prologues fill fk's addresses and family in place (ports belong to the L4 parser; fk must
+// be zero on entry so the v4 path leaves src[4:]/dst[4:] clear for map equality) and return pkt
+// trimmed to the IP-declared length. The receiver-as-out-pointer shape is deliberate: these
+// functions are too big to inline, and returning structs by value put five 64-byte copies on the
+// per-packet path.
+func (fk *flowKey) parseIPAt(pkt []byte, ipHdrLen int) ([]byte, bool) {
+	if len(pkt) < 20 {
+		return nil, false
+	}
+	switch pkt[0] >> 4 {
+	case 4:
+		if ipHdrLen != 20 {
+			return nil, false
+		}
+		return fk.parseIPv4Prologue(pkt)
+	case 6:
+		if ipHdrLen != 40 || len(pkt) < 40 {
+			return nil, false
+		}
+		return fk.parseIPv6Prologue(pkt)
+	}
+	return nil, false
+}
+
+// parseIPv4Prologue is the shared IPv4 tail of the prologue entries; the caller has verified
+// len(pkt) >= 20 and the version.
+func (fk *flowKey) parseIPv4Prologue(pkt []byte) ([]byte, bool) {
+	ihl := int(pkt[0]&0x0f) * 4
+	if ihl != 20 {
+		return nil, false
+	}
+	// Reject any fragmentation (MF or nonzero offset). The dispatcher already gated FragAny; kept
+	// as defense in depth, since a fragment folded into a superpacket would corrupt reassembly.
+	if binary.BigEndian.Uint16(pkt[6:8])&0x3fff != 0 {
+		return nil, false
+	}
+	totalLen := int(binary.BigEndian.Uint16(pkt[2:4]))
+	if totalLen > len(pkt) || totalLen < ihl {
+		return nil, false
+	}
+	fk.isV6 = false
+	copy(fk.src[:4], pkt[12:16])
+	copy(fk.dst[:4], pkt[16:20])
+	return pkt[:totalLen], true
+}
+
+// parseIPv6Prologue is the shared IPv6 tail; the caller has verified len(pkt) >= 40, the version,
+// and that the L4 header sits at byte 40.
+func (fk *flowKey) parseIPv6Prologue(pkt []byte) ([]byte, bool) {
+	payloadLen := int(binary.BigEndian.Uint16(pkt[4:6]))
+	if 40+payloadLen > len(pkt) {
+		return nil, false
+	}
+	fk.isV6 = true
+	copy(fk.src[:], pkt[8:24])
+	copy(fk.dst[:], pkt[24:40])
+	return pkt[:40+payloadLen], true
+}
+
+// ipHeadersMatch compares the IP portion of two packet header prefixes for
+// byte-for-byte equality on every field that must be identical across coalesced segments.
+// Size/IPID/IPCsum are masked out.
+// The full DSCP/ECN byte (IPv4 ToS / IPv6 traffic class) is compared, matching Linux kernel GRO:
+// segments with differing ECN codepoints must not coalesce,
+// otherwise ORing e.g. ECT(0) with ECT(1) would fabricate a false CE (congestion) mark or mark a Not-ECT flow as ECN-capable.
+//
+// The transport (L4) portion of the header is checked separately by the per-protocol matcher.
+func ipHeadersMatch(a, b []byte, isV6 bool) bool {
+	if isV6 {
+		// IPv6: [0:4] = version/TC/flow label (TC[1:0] is ECN, so the full TC byte must match),
+		// [6:40] = next_hdr/hop + src + dst. Skip [4:6] payload_len.
+		return bytes.Equal(a[:4], b[:4]) && bytes.Equal(a[6:40], b[6:40])
+	}
+	// IPv4: [0:2] = version/IHL + DSCP|ECN (full ECN byte must match),
+	// [6:10] = flags/fragoff/TTL/proto, [12:20] = src+dst.
+	// Skip [2:4] total len, [4:6] id, [10:12] csum.
+	return bytes.Equal(a[:2], b[:2]) && bytes.Equal(a[6:10], b[6:10]) && bytes.Equal(a[12:20], b[12:20])
+}
+
+// ipv4FlagDF is the Don't Fragment bit in the IPv4 flags byte (header byte 6).
+const ipv4FlagDF = 0x40
+
+// ipv4CanCoalesceID reports whether an IPv4 packet whose header starts at
+// nextHdr may join a chain whose seed header is seedHdr as segment index seg
+// (the seed is segment 0). Kernel GSO re-stamps outgoing segment IDs as
+// seed_id+n, so coalescing is only transparent when that re-stamp is either
+// harmless (DF set: RFC 6864 atomic datagrams, the ID carries no meaning) or
+// reproduces the original IDs exactly (DF clear + IDs already sequential —
+// the same admission rule kernel GRO applies). Without this, a DF=0 sender
+// with non-sequential IDs (e.g. OpenBSD's randomized IDs) could have IDs
+// rewritten into ranges that collide across superpackets, corrupting
+// reassembly if the packets are fragmented after the TUN write.
+//
+// DF itself is guaranteed uniform across a chain by ipHeadersMatch (byte 6
+// is inside its compared range), so checking the seed's copy suffices.
+func ipv4CanCoalesceID(seedHdr, nextHdr []byte, seg int) bool {
+	if seedHdr[6]&ipv4FlagDF != 0 {
+		return true
+	}
+	expect := binary.BigEndian.Uint16(seedHdr[4:6]) + uint16(seg)
+	return binary.BigEndian.Uint16(nextHdr[4:6]) == expect
+}
+
+// Arena is an injectable byte-slab that hands out non-overlapping borrowed
+// slices via Reserve and releases them in bulk via Reset.
+type Arena struct {
+	buf []byte
+}
+
+// NewArena returns an Arena with a pre-allocated backing of the given capacity.
+func NewArena(capacity int) *Arena {
+	return &Arena{buf: make([]byte, 0, capacity)}
+}
+
+// Reserve hands out a non-overlapping sz-byte slice from the arena.
+// If the request doesn't fit the current backing, a fresh, larger backing is allocated.
+// Already-borrowed slices reference the old backing and remain valid until Reset.
+func (a *Arena) Reserve(sz int) []byte {
+	if len(a.buf)+sz > cap(a.buf) {
+		newCap := max(cap(a.buf)*2, sz)
+		a.buf = make([]byte, 0, newCap)
+	}
+	start := len(a.buf)
+	a.buf = a.buf[:start+sz]
+	return a.buf[start : start+sz : start+sz]
+}
+
+// Reset releases every slice handed out since the last Reset.
+// Callers must not use any previously-borrowed slice after this returns.
+// The underlying backing array is retained so subsequent Reserves don't re-allocate.
+func (a *Arena) Reset() {
+	a.buf = a.buf[:0]
+}

overlay/batch/dispatch_bench_test.go

@@ -0,0 +1,112 @@
+package batch
+
+import (
+	"testing"
+
+	"github.com/slackhq/nebula/test"
+)
+
+// stagePackets builds the stagedPacket entries Commit would have produced, so dispatch benchmarks
+// bypass staging and the sort entirely.
+func stagePackets(pkts [][]byte) []stagedPacket {
+	staged := make([]stagedPacket, len(pkts))
+	for i, p := range pkts {
+		pp := testPP(p)
+		staged[i] = stagedPacket{
+			pkt:      p,
+			key:      SortKey{Epoch: 1, Counter: uint64(i + 1)},
+			proto:    pp.Protocol,
+			fragAny:  pp.FragAny,
+			ipHdrLen: uint16(pp.IPHdrLen),
+		}
+	}
+	return staged
+}
+
+func flushLanes(b *testing.B, m *MultiCoalescer) {
+	b.Helper()
+	if m.tcp != nil {
+		if err := m.tcp.Flush(); err != nil {
+			b.Fatal(err)
+		}
+	}
+	if m.udp != nil {
+		if err := m.udp.Flush(); err != nil {
+			b.Fatal(err)
+		}
+	}
+	if err := m.pt.Flush(); err != nil {
+		b.Fatal(err)
+	}
+}
+
+// runDispatchBench measures dispatch plus the per-batch lane flush: the post-sort half of the
+// batcher, which is where the production profile concentrates.
+func runDispatchBench(b *testing.B, pkts [][]byte, batchSize int) {
+	b.Helper()
+	m := NewMultiCoalescer(nopTunWriter{}, test.NewLogger())
+	staged := stagePackets(pkts)
+	b.ReportAllocs()
+	b.SetBytes(int64(len(pkts[0])))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		if err := m.dispatch(staged[i%len(staged)]); err != nil {
+			b.Fatal(err)
+		}
+		if (i+1)%batchSize == 0 {
+			flushLanes(b, m)
+		}
+	}
+	b.StopTimer()
+	flushLanes(b, m)
+}
+
+// BenchmarkDispatchSingleFlow is the bulk steady state: every packet past the seed appends.
+func BenchmarkDispatchSingleFlow(b *testing.B) {
+	runDispatchBench(b, buildTCPv4BulkFlow(tcpCoalesceMaxSegs, 1200), tcpCoalesceMaxSegs)
+}
+
+// BenchmarkDispatchInterleaved16 stresses the openSlots map: 16 flows round-robined defeats the
+// lastSlot cache on every packet.
+func BenchmarkDispatchInterleaved16(b *testing.B) {
+	pkts := buildTCPv4Interleaved(16, tcpCoalesceMaxSegs, 1200)
+	runDispatchBench(b, pkts, len(pkts))
+}
+
+// BenchmarkDispatchAckHeavy alternates MSS data with pure ACKs on one flow — the RX shape of a
+// bidirectional transfer (the peer's data and its ACKs of our data share the tunnel direction).
+func BenchmarkDispatchAckHeavy(b *testing.B) {
+	pay := make([]byte, 1200)
+	var pkts [][]byte
+	seq := uint32(1000)
+	for range tcpCoalesceMaxSegs / 2 {
+		pkts = append(pkts, buildTCPv4(seq, tcpAck, pay))
+		seq += uint32(len(pay))
+		pkts = append(pkts, buildTCPv4(seq, tcpAck, nil))
+	}
+	runDispatchBench(b, pkts, len(pkts))
+}
+
+// BenchmarkDispatchUDPFlow is the QUIC-ish bulk UDP shape.
+func BenchmarkDispatchUDPFlow(b *testing.B) {
+	pay := make([]byte, 1200)
+	pkts := make([][]byte, udpCoalesceMaxSegs)
+	for i := range pkts {
+		pkts[i] = buildUDPv4(2000, 443, pay)
+	}
+	runDispatchBench(b, pkts, len(pkts))
+}
+
+// BenchmarkDispatchSeedHeavy sets PSH on every packet so each one seeds and immediately closes
+// its own slot — the small-write RPC shape, and the upper bound on what the seed path (including
+// the parsedTCP-to-slot field transfer) can cost.
+func BenchmarkDispatchSeedHeavy(b *testing.B) {
+	pay := make([]byte, 1200)
+	pkts := make([][]byte, tcpCoalesceMaxSegs)
+	seq := uint32(1000)
+	for i := range pkts {
+		pkts[i] = buildTCPv4(seq, tcpAckPsh, pay)
+		seq += uint32(len(pay))
+	}
+	runDispatchBench(b, pkts, len(pkts))
+}

overlay/batch/lane_entry_test.go

@@ -0,0 +1,76 @@
+package batch
+
+//TODO refactor this away
+// This file holds the lanes' self-parsing Commit entries and the proto-checking parsers behind
+// them. Production traffic enters the lanes only through MultiCoalescer.dispatch and the At
+// parsers; these wrappers reproduce that path (including seal-all on unparseable shapes) on top
+// of a local parse, so tests and benches can drive one lane with nothing but a packet.
+
+// parseIPPrologue resolves the IP version, requires the L4 protocol to match wantProto (6 TCP,
+// 17 UDP), and defers to the shared per-version cores. Returns the trimmed packet and the L4
+// offset; fk must be zero on entry and is filled in place.
+func (fk *flowKey) parseIPPrologue(pkt []byte, wantProto byte) ([]byte, int, bool) {
+	if len(pkt) < 20 {
+		return nil, 0, false
+	}
+	switch pkt[0] >> 4 {
+	case 4:
+		if pkt[9] != wantProto {
+			return nil, 0, false
+		}
+		trimmed, ok := fk.parseIPv4Prologue(pkt)
+		return trimmed, 20, ok
+	case 6:
+		if len(pkt) < 40 {
+			return nil, 0, false
+		}
+		if pkt[6] != wantProto {
+			return nil, 0, false
+		}
+		trimmed, ok := fk.parseIPv6Prologue(pkt)
+		return trimmed, 40, ok
+	}
+	return nil, 0, false
+}
+
+// parseBase extracts the flow key and IP/TCP offsets for any TCP packet, admissible for
+// coalescing or not. Returns false for non-TCP or malformed input.
+func (p *parsedTCP) parseBase(pkt []byte) bool {
+	trimmed, ipHdrLen, ok := p.fk.parseIPPrologue(pkt, ipProtoTCP)
+	if !ok {
+		return false
+	}
+	return p.parseTail(trimmed, ipHdrLen)
+}
+
+// parseBase extracts the flow key and IP/UDP offsets for a UDP packet.
+func (p *parsedUDP) parseBase(pkt []byte) bool {
+	trimmed, ipHdrLen, ok := p.fk.parseIPPrologue(pkt, ipProtoUDP)
+	if !ok {
+		return false
+	}
+	return p.parseTail(trimmed, ipHdrLen)
+}
+
+// Commit borrows pkt. The caller must keep pkt valid until the next Flush.
+func (c *TCPCoalescer) Commit(pkt []byte) error {
+	var info parsedTCP
+	if !info.parseBase(pkt) {
+		// Unparseable: flow key unknown, seal everything so later data cannot emit ahead of it.
+		c.sealAllOpen()
+		c.addVerbatim(pkt)
+		return nil
+	}
+	return c.commitParsed(pkt, &info)
+}
+
+// Commit borrows pkt. The caller must keep pkt valid until the next Flush.
+func (c *UDPCoalescer) Commit(pkt []byte) error {
+	var info parsedUDP
+	if !info.parseBase(pkt) {
+		c.sealAllOpen()
+		c.addVerbatim(pkt)
+		return nil
+	}
+	return c.commitParsed(pkt, &info)
+}

overlay/batch/multi_coalesce.go

@@ -0,0 +1,133 @@
+package batch
+
+import (
+	"cmp"
+	"errors"
+	"io"
+	"log/slog"
+	"slices"
+
+	"github.com/slackhq/nebula/firewall"
+)
+
+// MultiCoalescer stages plaintext packets with their (epoch, counter) sort keys and, at Flush,
+// replays them in sender-transmission order into lane-specific batchers selected by L4 protocol.
+//
+// Sorting before dispatch keeps the ordering story simple: each lane consumes packets in
+// transmission order, builds slots in that order, and emits them in creation order. Wire reorder
+// inside a flush batch is repaired here, before it can fragment a lane's coalesce chains, so the
+// lanes carry no reorder-repair machinery.
+//
+// The contract is per-tunnel transmission order within each lane, with two exceptions: a pure TCP
+// ACK may be overtaken by later same-flow data (it does not close the flow's open chain; a late
+// ACK is just a stale ACK), and an unparseable shape seals every open chain in its lane (its flow
+// is unknown) and rides the lane as an in-lane verbatim, still in transmission order. Routing
+// follows the flow: a flow's non-coalesceable shapes ride its protocol lane rather than falling
+// to the later-flushed pt lane.
+//
+// Cross-lane order (TCP vs UDP vs everything else) is not preserved.
+type MultiCoalescer struct {
+	tcp *TCPCoalescer
+	udp *UDPCoalescer
+	pt  *Passthrough
+
+	// staged holds this batch's packets and sort keys until Flush. Borrowed: the caller keeps
+	// each pkt alive until Flush returns.
+	staged []stagedPacket
+}
+
+// stagedPacket carries the scalars dispatch needs from the firewall's ParsedPacket, copied by
+// value: pp is reused by the caller per packet and must not be retained past Commit.
+type stagedPacket struct {
+	pkt      []byte
+	key      SortKey
+	proto    byte
+	fragAny  bool
+	ipHdrLen uint16
+}
+
+// NewMultiCoalescer builds a multi-lane batcher over w, based on available protocol support. The
+// staging sort applies even when no GSO lane is available: passthrough-only platforms still get
+// transmission-order repair.
+func NewMultiCoalescer(w io.Writer, l *slog.Logger) *MultiCoalescer {
+	m := &MultiCoalescer{
+		pt:     NewPassthrough(w),
+		staged: make([]stagedPacket, 0, initialSlots),
+	}
+	m.tcp = NewTCPCoalescer(w, l)
+	m.udp = NewUDPCoalescer(w)
+	return m
+}
+
+// Commit stages pkt for the next Flush; dispatch is deferred so it runs on packets already in
+// transmission order. key carries the packet's tunnel epoch and message counter. pkt is borrowed:
+// the caller must keep it valid until the next Flush and not re-use it, and Flush may patch a
+// coalesced packet's headers in place. pp is the firewall's parse of pkt and is borrowed only
+// for this call, so the fields dispatch needs are copied here.
+func (m *MultiCoalescer) Commit(pkt []byte, key SortKey, pp *firewall.ParsedPacket) error {
+	m.staged = append(m.staged, stagedPacket{
+		pkt:      pkt,
+		key:      key,
+		proto:    pp.Protocol,
+		fragAny:  pp.FragAny,
+		ipHdrLen: uint16(pp.IPHdrLen),
+	})
+	return nil
+}
+
+// compareStaged orders staged packets by (epoch, counter)
+func compareStaged(a, b stagedPacket) int {
+	if c := cmp.Compare(a.key.Epoch, b.key.Epoch); c != 0 {
+		return c
+	}
+	return cmp.Compare(a.key.Counter, b.key.Counter)
+}
+
+// dispatch routes one staged packet to its protocol lane (see commitStaged), or to the verbatim
+// passthrough when the lane has no GSO support.
+func (m *MultiCoalescer) dispatch(sp stagedPacket) error {
+	switch sp.proto {
+	case ipProtoTCP:
+		if m.tcp != nil {
+			return m.tcp.commitStaged(sp)
+		}
+	case ipProtoUDP:
+		if m.udp != nil {
+			return m.udp.commitStaged(sp)
+		}
+	}
+	return m.pt.enqueue(sp.pkt)
+}
+
+// Flush sorts the staged batch into transmission order, replays it into the lanes, then flushes each lane.
+// Drains everything and returns the joined errors; one bad packet does not hold up the rest.
+// After Flush returns, committed payload slices may be recycled.
+func (m *MultiCoalescer) Flush() error {
+	// Arrival order is already almost sorted (reorder is the exception), which pdqsort detects
+	// and handles in near-linear time.
+	slices.SortFunc(m.staged, compareStaged)
+
+	var errs []error
+	for _, sp := range m.staged {
+		if err := m.dispatch(sp); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	clear(m.staged) // drop borrowed pkt refs
+	m.staged = m.staged[:0]
+
+	if m.tcp != nil {
+		if err := m.tcp.Flush(); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	if m.udp != nil {
+		if err := m.udp.Flush(); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	if err := m.pt.Flush(); err != nil {
+		errs = append(errs, err)
+	}
+	return errors.Join(errs...)
+}