BGP: Implement RFC6286

  RFC6286, Autonomous-System-Wide Unique BGP Identifier for BGP-4, loosens the
  requirements for Router IDs to allow for IPv6-only setups.

Signed-off-by: Maximilian Wilhelm <[email protected]>

RFCs.md

@@ -7,6 +7,7 @@ Please keep this list ordered.
  * 4271 A Border Gateway Protocol 4 (BGP-4)
  * 4456 BGP Route Reflection
  * 4760 Multiprotocol Extensions for BGP-4
+ * 6286 Autonomous-System-Wide Unique BGP Identifier for BGP-4
  * 6793 32bit ASNs
  * 7854 BGP Monitoring Protocol (BMP)
  * 7911 BGP AddPath

protocols/bgp/server/fsm_open_sent.go

@@ -124,6 +124,14 @@ func (s *openSentState) openMsgReceived(openMsg *packet.BGPOpen) (state, string)
 		return s.handleOpenMessage(openMsg)
 	}
 
+	// RFC6286, Sect 2.2: If the BGP Identifier field of the OPEN message is zero,
+	// or if it is the same as the BGP Identifier of the local BGP speaker and the
+	// message is from an internal peer, then the Error Subcode is set to "Bad BGP Identifier".
+	if openMsg.BGPIdentifier == 0 || (s.fsm.peer.localASN == s.fsm.peer.peerASN && s.fsm.peer.routerID == openMsg.BGPIdentifier) {
+		s.fsm.sendNotification(packet.OpenMessageError, packet.BadBGPIdentifier)
+		return newIdleState(s.fsm), fmt.Sprintf("Bad BGP Identifier %d", openMsg.BGPIdentifier)
+	}
+
 	stopTimer(s.fsm.connectRetryTimer)
 	if s.fsm.peer.collisionHandling(s.fsm) {
 		return s.cease()

protocols/bgp/server/peer.go

@@ -234,7 +234,7 @@ func (p *peer) collisionHandling(callingFSM *FSM) bool {
 			continue
 		}
 
-		if p.routerID < callingFSM.neighborID {
+		if p.shouldCeaseOnCollision(callingFSM) {
 			fsm.cease()
 		} else {
 			return true
@@ -244,6 +244,24 @@ func (p *peer) collisionHandling(callingFSM *FSM) bool {
 	return false
 }
 
+func (p *peer) shouldCeaseOnCollision(callingFSM *FSM) bool {
+	// RFC6286: For a BGP speaker that supports the AS-wide Unique BGP Identifier,
+	// the procedures for connection collision resolution are extended as
+	// follows to deal with the case in which the two BGP speakers share the
+	// same BGP Identifier (thus, it is only applicable to an external
+	// peer):
+	//
+	//    If the BGP Identifiers of the peers involved in the connection
+	//    collision are identical, then the connection initiated by the BGP
+	//    speaker with the larger AS number is preserved.
+	if p.routerID == callingFSM.neighborID {
+		return p.localASN < callingFSM.peer.peerASN
+	}
+
+	// RFC4271 collision handling
+	return p.routerID < callingFSM.neighborID
+}
+
 func isOpenConfirmState(s state) bool {
 	switch s.(type) {
 	case openConfirmState: