From a4d5d004cc3d97c90de0c2d91f2312525e055d68 Mon Sep 17 00:00:00 2001
From: Jordan Whited <jwhited@subspace.com>
Date: Mon, 10 Aug 2020 09:43:54 -0700
Subject: best path selection - compare neigh addr

---
 internal/pkg/table/destination.go      | 31 +++++++++++++++++++++++++++++++
 internal/pkg/table/destination_test.go | 22 ++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/internal/pkg/table/destination.go b/internal/pkg/table/destination.go
index 2880f662..0b438d78 100644
--- a/internal/pkg/table/destination.go
+++ b/internal/pkg/table/destination.go
@@ -50,6 +50,7 @@ const (
 	BPR_ROUTER_ID
 	BPR_OLDER
 	BPR_NON_LLGR_STALE
+	BPR_NEIGH_ADDR
 )
 
 var BestPathReasonStringMap = map[BestPathReason]string{
@@ -68,6 +69,7 @@ var BestPathReasonStringMap = map[BestPathReason]string{
 	BPR_ROUTER_ID:          "Router ID",
 	BPR_OLDER:              "Older",
 	BPR_NON_LLGR_STALE:     "no LLGR Stale",
+	BPR_NEIGH_ADDR:         "Neighbor Address",
 }
 
 func (r *BestPathReason) String() string {
@@ -480,6 +482,10 @@ func (dst *Destination) sort() BestPathReason {
 			}
 			reason = BPR_ROUTER_ID
 		}
+		if better == nil {
+			better = compareByNeighborAddress(path1, path2)
+			reason = BPR_NEIGH_ADDR
+		}
 		if better == nil {
 			reason = BPR_UNKNOWN
 			better = path1
@@ -918,6 +924,31 @@ func compareByRouterID(path1, path2 *Path) (*Path, error) {
 	}
 }
 
+func compareByNeighborAddress(path1, path2 *Path) *Path {
+	// Select the route received from the peer with the lowest peer address as
+	// per RFC 4271 9.1.2.2. g
+	log.WithFields(log.Fields{
+		"Topic": "Table",
+	}).Debug("enter compareByNeighborAddress")
+
+	p1 := path1.GetSource().Address
+	if p1 == nil {
+		return path1
+	}
+	p2 := path2.GetSource().Address
+	if p2 == nil {
+		return path2
+	}
+
+	cmp := bytes.Compare(p1, p2)
+	if cmp < 0 {
+		return path1
+	} else if cmp > 0 {
+		return path2
+	}
+	return nil
+}
+
 func compareByAge(path1, path2 *Path) *Path {
 	if !path1.IsIBGP() && !path2.IsIBGP() && !SelectionOptions.ExternalCompareRouterId {
 		age1 := path1.GetTimestamp().UnixNano()
diff --git a/internal/pkg/table/destination_test.go b/internal/pkg/table/destination_test.go
index b1c1b2e8..3534cb6c 100644
--- a/internal/pkg/table/destination_test.go
+++ b/internal/pkg/table/destination_test.go
@@ -118,6 +118,28 @@ func TestCalculate2(t *testing.T) {
 	assert.Equal(t, len(d.knownPathList), 3)
 }
 
+func TestNeighAddrTieBreak(t *testing.T) {
+	nlri := bgp.NewIPAddrPrefix(24, "10.10.0.0")
+
+	peer0 := &PeerInfo{AS: 65001, LocalAS: 1, Address: net.IP{2, 2, 2, 2}, ID: net.IP{2, 2, 2, 2}}
+
+	p0 := func() *Path {
+		aspath := bgp.NewPathAttributeAsPath([]bgp.AsPathParamInterface{bgp.NewAs4PathParam(bgp.BGP_ASPATH_ATTR_TYPE_SEQ, []uint32{65001})})
+		attrs := []bgp.PathAttributeInterface{aspath, bgp.NewPathAttributeMultiExitDisc(0)}
+		return NewPath(peer0, nlri, false, attrs, time.Now(), false)
+	}()
+
+	peer1 := &PeerInfo{AS: 65001, LocalAS: 1, Address: net.IP{3, 3, 3, 3}, ID: net.IP{2, 2, 2, 2}} // same ID as peer0, separate eBGP session
+
+	p1 := func() *Path {
+		aspath := bgp.NewPathAttributeAsPath([]bgp.AsPathParamInterface{bgp.NewAs4PathParam(bgp.BGP_ASPATH_ATTR_TYPE_SEQ, []uint32{65001})})
+		attrs := []bgp.PathAttributeInterface{aspath, bgp.NewPathAttributeMultiExitDisc(0)}
+		return NewPath(peer1, nlri, false, attrs, time.Now(), false)
+	}()
+
+	assert.Equal(t, compareByNeighborAddress(p0, p1), p0)
+}
+
 func TestMedTieBreaker(t *testing.T) {
 	nlri := bgp.NewIPAddrPrefix(24, "10.10.0.0")
 
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