server: use configured local address for nexthop when set#3420
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When Transport.Config.LocalAddress is set to a specific (non-wildcard) address, override Transport.State.LocalAddress with it instead of using the TCP connection's local address. This ensures the configured address is advertised as the BGP nexthop. This is needed for deployments where the BGP listener binds to an internal address (e.g. VRFs over GENEVE tunnels) but the configured local address is what should be advertised as the nexthop. The override is applied in handleFSMMessage() via ReadCopy/Update on pConf before NewPeerInfo is created, so all downstream consumers (toConfig, prePolicyFilterpath nexthop rewrite, watch events) automatically read the correct value. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
When
Transport.Config.LocalAddressis set to a specific (non-wildcard) address, overrideTransport.State.LocalAddresswith it instead of using the TCP connection's local address. This ensures the configured address is advertised as the BGP nexthop.This is needed for deployments where the BGP listener binds to an internal address (e.g., VRFs over GENEVE tunnels) but the configured local address is what should be advertised as the nexthop. Without this fix, the TCP connection's local address (the listener's bind address) is used, resulting in incorrect nexthop advertisement.
Background
This issue was originally addressed in #2827 and #2839 (both closed). The fix was applied to downstream forks and evolved with IPv6 improvements, but was inadvertently removed during two upstream refactoring commits:
075aab46("convert PeerInfo to use netip instead of net", Aug 2025) removed the override fromhandleFSMMessage0c74e9c6("server: remove access to fsm.conn in server", Oct 2025) removed the override fromtoConfigApproach
The override is applied in
server.go:handleFSMMessage()when a session reaches ESTABLISHED, consistent with the original PRs. It uses the standardReadCopy → modify → Updatepattern underfsm.lockto persist the overridden address topConfbeforeNewPeerInfois created. All downstream consumers (toConfig,prePolicyFilterpath/nexthop rewrite, watch events) read fromTransport.Stateand automatically get the correct value.The override only applies when the configured address is valid and non-unspecified (not
0.0.0.0or::). IPv6 zone information is stripped since BGP nexthop attributes cannot carry zone info.Test plan
TestLocalAddressOverrideintegration test with 3 sub-tests that establish a real two-server BGP session and verify the overridden address via theListPeerAPI:0.0.0.0(no override)BindInterfaceset (override applied)go build ./...passesgo vet ./pkg/server/...passesgo test -race ./pkg/server/...passes🤖 Generated with Claude Code