fix stuck route

2 files changed, 27 insertions, 2 deletions

diff --git a/pkg/server/peer.go b/pkg/server/peer.go
index a3f2be7b..4a7d5922 100644
--- a/pkg/server/peer.go
+++ b/pkg/server/peer.go
@@ -131,6 +131,15 @@ func (peer *peer) ID() string {
 	return peer.fsm.pConf.State.NeighborAddress
 }
 
+func (peer *peer) RouterID() string {
+	peer.fsm.lock.RLock()
+	defer peer.fsm.lock.RUnlock()
+	if peer.fsm.peerInfo.ID != nil {
+		return peer.fsm.peerInfo.ID.String()
+	}
+	return ""
+}
+
 func (peer *peer) TableID() string {
 	return peer.tableId
 }
@@ -348,7 +357,22 @@ func (peer *peer) stopPeerRestarting() {
 }
 
 func (peer *peer) filterPathFromSourcePeer(path, old *table.Path) *table.Path {
-	if peer.ID() != path.GetSource().Address.String() {
+	// Consider 3 peers - A, B, C and prefix P originated by C. Parallel eBGP
+	// sessions exist between A & B, and both have a single session with C.
+	//
+	// When A receives the withdraw from C, we enter this func for each peer of
+	// A, with the following:
+	// peer: [C, B #1, B #2]
+	// path: new best for P facing B
+	// old: old best for P facing C
+	//
+	// Our comparison between peer identifier and path source ID must be router
+	// ID-based (not neighbor address), otherwise we will return early. If we
+	// return early for one of the two sessions facing B
+	// (whichever is not the new best path), we fail to send a withdraw towards
+	// B, and the route is "stuck".
+	// TODO: considerations for RFC6286
+	if peer.RouterID() != path.GetSource().ID.String() {
 		return path
 	}
 
diff --git a/pkg/server/server_test.go b/pkg/server/server_test.go
index 6f70f38a..39b10657 100644
--- a/pkg/server/server_test.go
+++ b/pkg/server/server_test.go
@@ -706,10 +706,11 @@ func newPeerandInfo(myAs, as uint32, address string, rib *table.TableManager) (*
 		nConf,
 		rib,
 		policy)
+	p.fsm.peerInfo.ID = net.ParseIP(address)
 	for _, f := range rib.GetRFlist() {
 		p.fsm.rfMap[f] = bgp.BGP_ADD_PATH_NONE
 	}
-	return p, &table.PeerInfo{AS: as, Address: net.ParseIP(address)}
+	return p, &table.PeerInfo{AS: as, Address: net.ParseIP(address), ID: net.ParseIP(address)}
 }
 
 func process(rib *table.TableManager, l []*table.Path) (*table.Path, *table.Path) {