server: apply TCP-AO to peer sockets

internal/pkg/netutils/sockopt.go

@@ -56,7 +56,7 @@ func SetReuseAddrSockopt(sc syscall.RawConn) error {
 	return SetReuseAddrSockoptImpl(sc)
 }
 
-func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, minTtl uint8, mss uint16, password string, bindInterface string, tos uint8) error {
+func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, minTtl uint8, mss uint16, password string, bindInterface string, tos uint8, tcpAO *TCPAOConfig) error {
 	if password != "" {
 		logger.Warn("setting md5 for active connection is not supported",
 			slog.String("Topic", "Peer"),
@@ -87,5 +87,8 @@ func DialerControl(logger *slog.Logger, network, address string, c syscall.RawCo
 			slog.String("Key", address),
 		)
 	}
+	if tcpAO != nil {
+		return ErrTCPAONotSupported
+	}
 	return nil
 }

internal/pkg/netutils/sockopt_linux.go

@@ -180,7 +180,7 @@ func SetReuseAddrSockopt(sc syscall.RawConn) error {
 	return setSockOptInt(sc, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
 }
 
-func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, minTtl uint8, mss uint16, password string, bindInterface string, tos uint8) error {
+func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, minTtl uint8, mss uint16, password string, bindInterface string, tos uint8, tcpAO *TCPAOConfig) error {
 	family := syscall.AF_INET
 	raddr, _ := net.ResolveTCPAddr("tcp", address)
 	if raddr.IP.To4() == nil {
@@ -280,5 +280,16 @@ func DialerControl(logger *slog.Logger, network, address string, c syscall.RawCo
 			return sockerr
 		}
 	}
+
+	if tcpAO != nil {
+		addrPort, err := netip.ParseAddrPort(address)
+		if err != nil {
+			return fmt.Errorf("invalid TCP-AO peer address %q: %w", address, err)
+		}
+		addr := addrPort.Addr().Unmap()
+		if err := AddTCPAOKeysSockopt(c, netip.PrefixFrom(addr, addr.BitLen()), bindInterface, *tcpAO); err != nil {
+			return fmt.Errorf("failed to configure TCP-AO for peer %s: %w", addr, err)
+		}
+	}
 	return nil
 }

internal/pkg/netutils/sockopt_openbsd.go

@@ -422,7 +422,7 @@ func SetReuseAddrSockopt(sc syscall.RawConn) error {
 	return setSockOptInt(sc, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
 }
 
-func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, minTtl uint8, mss uint16, password string, bindInterface string, tos uint8) error {
+func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, minTtl uint8, mss uint16, password string, bindInterface string, tos uint8, tcpAO *TCPAOConfig) error {
 	family := syscall.AF_INET
 	raddr, _ := net.ResolveTCPAddr("tcp", address)
 	if raddr.IP.To4() == nil {
@@ -472,5 +472,8 @@ func DialerControl(logger *slog.Logger, network, address string, c syscall.RawCo
 			return sockerr
 		}
 	}
+	if tcpAO != nil {
+		return ErrTCPAONotSupported
+	}
 	return nil
 }

internal/pkg/netutils/sockopt_windows.go

@@ -94,7 +94,7 @@ func SetReuseAddrSockopt(sc syscall.RawConn) error {
 	return setSockOptInt(sc, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
 }
 
-func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, ttlMin uint8, mss uint16, password string, bindInterface string, tos uint8) error {
+func DialerControl(logger *slog.Logger, network, address string, c syscall.RawConn, ttl, ttlMin uint8, mss uint16, password string, bindInterface string, tos uint8, tcpAO *TCPAOConfig) error {
 	if password != "" {
 		logger.Warn("setting md5 for active connection is not supported",
 			slog.String("Topic", "Peer"),
@@ -120,5 +120,8 @@ func DialerControl(logger *slog.Logger, network, address string, c syscall.RawCo
 			slog.String("Topic", "Peer"),
 			slog.String("Key", address))
 	}
+	if tcpAO != nil {
+		return ErrTCPAONotSupported
+	}
 	return nil
 }

internal/pkg/netutils/tcp_ao_linux_test.go

@@ -19,6 +19,7 @@ package netutils
 import (
 	"context"
 	"errors"
+	"log/slog"
 	"net"
 	"net/netip"
 	"syscall"
@@ -173,9 +174,8 @@ func TestTCPAOKeySelection(t *testing.T) {
 		PreferredSendID: &current,
 	}
 	dialer := net.Dialer{Timeout: time.Second}
-	dialer.SetMultipathTCP(false)
-	dialer.Control = func(_, _ string, raw syscall.RawConn) error {
-		return AddTCPAOKeysSockopt(raw, peer, "", clientConfig)
+	dialer.Control = func(network, address string, raw syscall.RawConn) error {
+		return DialerControl(slog.Default(), network, address, raw, 0, 0, 0, "", "", 0, &clientConfig)
 	}
 	clientConn, err := dialer.DialContext(context.Background(), "tcp4", listener.Addr().String())
 	require.NoError(t, err)

pkg/config/oc/util.go

@@ -226,7 +226,8 @@ func (n *Neighbor) NeedsResendOpenMessage(new *Neighbor) bool {
 		!n.GracefulRestart.Config.Equal(&new.GracefulRestart.Config) ||
 		isAfiSafiChanged(n.AfiSafis, new.AfiSafis) ||
 		!n.EbgpMultihop.Config.Equal(&new.EbgpMultihop.Config) ||
-		!n.TtlSecurity.Config.Equal(&new.TtlSecurity.Config)
+		!n.TtlSecurity.Config.Equal(&new.TtlSecurity.Config) ||
+		n.TcpAo.Config.Keychain != new.TcpAo.Config.Keychain
 }
 
 // TODO: these regexp are duplicated in api

pkg/server/fsm.go

@@ -417,6 +417,20 @@ func (p *pConfAccess) Update(conf *oc.Neighbor) {
 	p.conf.Store(conf)
 }
 
+// tcpAoKeyBinding is a peer's resolved TCP-AO configuration:
+// a reference to a shared keychain plus the peer's preferred send ID.
+//
+// Keychain's key additions and deletions mutate the shared keychain under its lock,
+// socketKeys() can be used to take live key snapshots for socket operations.
+type tcpAoKeyBinding struct {
+	keychain        *tcpAoKeychain
+	preferredSendID uint8
+}
+
+func (b *tcpAoKeyBinding) socketKeys() (*tcpAoSocketKeys, error) {
+	return b.keychain.socketKeys(b.preferredSendID)
+}
+
 type fsm struct {
 	counterStats oc.Messages
 	timerStats   oc.Timers
@@ -450,6 +464,16 @@ type fsm struct {
 	adminStateCh             chan adminStateOperation
 	outgoingConnCh           chan outgoingConn
 
+	// tcpAoKeyBinding holds resolved TCP-AO configuration for the peer:
+	// - Passive peers have all configured keys installed on matching listening sockets;
+	//   preferred key is not set on the listener until an inbound connection is accepted and matched to the peer.
+	// - Active peers install all keys in net.Dialer.Control in connectLoop() and mark the preferred key during installation.
+	// - Async keychain update causes update of keys directly on the listening sockets and fsm conn sockets of the affected peers.
+	//   This is handled on best effort; keychain update is not rolled back upon individual socket operation errors.
+	// - Attaching, removing, or changing a keychain of a peer always uses peer delete-and-add path.
+	//   A preferred key change within the same keychain is handled live by updating RNext on the current connection.
+	tcpAoKeyBinding atomic.Pointer[tcpAoKeyBinding]
+
 	// only loop goroutine accesses; no lock required
 	outgoingConnMgr   *outgoingConnManager
 	idleHoldTime      float64
@@ -911,7 +935,7 @@ func (h *fsmHandler) idle(ctx context.Context) (bgp.FSMState, *fsmStateReason) {
 func (h *fsmHandler) connectLoop(ctx context.Context) net.Conn {
 	fsm := h.fsm
 
-	retryInterval, addr, port, password, ttl, ttlMin, mss, localAddress, localPort, bindInterface, tos := func() (int, string, int, string, uint8, uint8, uint16, string, int, string, uint8) {
+	retryInterval, addr, port, password, ttl, ttlMin, mss, localAddress, localPort, bindInterface, tos := func() (int, netip.Addr, int, string, uint8, uint8, uint16, string, int, string, uint8) {
 		conf := fsm.pConf.ReadOnly()
 		tick := max(int(conf.Timers.Config.ConnectRetry), minConnectRetryInterval)
 
@@ -937,7 +961,7 @@ func (h *fsmHandler) connectLoop(ctx context.Context) net.Conn {
 				ttl = conf.EbgpMultihop.Config.MultihopTtl
 			}
 		}
-		return tick, addr.String(), port, password, ttl, ttlMin, conf.Transport.Config.TcpMss, conf.Transport.Config.LocalAddress.String(), int(conf.Transport.Config.LocalPort), conf.Transport.Config.BindInterface, tos
+		return tick, addr, port, password, ttl, ttlMin, conf.Transport.Config.TcpMss, conf.Transport.Config.LocalAddress.String(), int(conf.Transport.Config.LocalPort), conf.Transport.Config.BindInterface, tos
 	}()
 
 	tick := minConnectRetryInterval
@@ -963,11 +987,22 @@ func (h *fsmHandler) connectLoop(ctx context.Context) net.Conn {
 				Timeout:   time.Duration(max(retryInterval-1, minConnectRetryInterval)) * time.Second,
 				KeepAlive: -1,
 				Control: func(network, address string, c syscall.RawConn) error {
-					return netutils.DialerControl(fsm.logger, network, address, c, ttl, ttlMin, mss, password, bindInterface, tos)
+					var tcpAO *netutils.TCPAOConfig
+					if keyBinding := fsm.tcpAoKeyBinding.Load(); keyBinding != nil {
+						tcpAoKeys, err := keyBinding.socketKeys()
+						if err != nil {
+							return fmt.Errorf("failed to load TCP-AO keychain for peer %s: %w", addr, err)
+						}
+						config, err := tcpAoKeys.netutilsConfig(true)
+						if err != nil {
+							return fmt.Errorf("failed to configure TCP-AO for peer %s: %w", addr, err)
+						}
+						tcpAO = &config
+					}
+					return netutils.DialerControl(fsm.logger, network, address, c, ttl, ttlMin, mss, password, bindInterface, tos, tcpAO)
 				},
 			}
-
-			conn, err := d.DialContext(ctx, "tcp", net.JoinHostPort(addr, strconv.Itoa(port)))
+			conn, err := d.DialContext(ctx, "tcp", net.JoinHostPort(addr.String(), strconv.Itoa(port)))
 			select {
 			case <-ctx.Done():
 				fsm.logger.Debug("stop connect loop")

pkg/server/fsm_test.go

@@ -554,7 +554,7 @@ func TestFsmPeerConfigAccess(t *testing.T) {
 		},
 	}
 
-	peer := newPeer(nil, &a, bgp.BGP_FSM_ESTABLISHED, nil, nil, slog.Default())
+	peer := newPeer(nil, &a, bgp.BGP_FSM_ESTABLISHED, nil, nil, nil, slog.Default())
 	b := peer.fsm.pConf.ReadCopy()
 
 	assert.True(t, a.Equal(&b))

pkg/server/peer.go

@@ -65,6 +65,12 @@ func (pg *peerGroup) DeleteDynamicNeighbor(prefix string) {
 }
 
 func newDynamicPeer(g *oc.Global, neighborAddress string, pg *oc.PeerGroup, loc *table.TableManager, policy *table.RoutingPolicy, logger *slog.Logger) *peer {
+	if pg.TcpAo.Config.Keychain != "" {
+		logger.Debug("TCP-AO dynamic neighbors are not supported",
+			slog.String("Topic", "Peer"),
+			slog.String("Key", neighborAddress))
+		return nil
+	}
 	conf := oc.Neighbor{
 		Config: oc.NeighborConfig{
 			PeerGroup: pg.Config.PeerGroupName,
@@ -93,7 +99,7 @@ func newDynamicPeer(g *oc.Global, neighborAddress string, pg *oc.PeerGroup, loc
 		return nil
 	}
 
-	return newPeer(g, &conf, bgp.BGP_FSM_ACTIVE, loc, policy, logger)
+	return newPeer(g, &conf, bgp.BGP_FSM_ACTIVE, loc, policy, nil, logger)
 }
 
 // pathIDSet is the set of add-path local identifiers advertised for a destination.
@@ -125,7 +131,7 @@ type peer struct {
 	routeRefreshInProgress sync.RWMutex
 }
 
-func newPeer(g *oc.Global, conf *oc.Neighbor, state bgp.FSMState, loc *table.TableManager, policy *table.RoutingPolicy, logger *slog.Logger) *peer {
+func newPeer(g *oc.Global, conf *oc.Neighbor, state bgp.FSMState, loc *table.TableManager, policy *table.RoutingPolicy, tcpAo *tcpAoKeyBinding, logger *slog.Logger) *peer {
 	peer := &peer{
 		localRib:          loc,
 		policy:            policy,
@@ -140,6 +146,7 @@ func newPeer(g *oc.Global, conf *oc.Neighbor, state bgp.FSMState, loc *table.Tab
 	rfs, _ := oc.AfiSafis(conf.AfiSafis).ToRfList()
 	peer.adjRibIn = table.NewAdjRib(logger, rfs)
 	peer.rtmHandler = table.NewRouteTargetMembershipHandler()
+	peer.fsm.tcpAoKeyBinding.Store(tcpAo)
 	return peer
 }