Use subset of rtarget eBGP paths when advertising vpn routes

Only consider paths that are learnt from same neighbor AS as
best eBGP path.

Note that different RTC routes for the same RT can and will
result in VPN routes being advertised to more than 1 AS. This
is correct behavior.

Change-Id: I7a08c452c9ee5788fdd615e58a096796752070e0
Closes-Bug: 1582933

src/bgp/bgp_path.cc

@@ -125,6 +125,15 @@ int BgpPath::PathCompare(const BgpPath &rhs, bool allow_ecmp) const {
     return 0;
 }
 
+bool BgpPath::PathSameNeighborAs(const BgpPath &rhs) const {
+    const BgpAttr *rattr = rhs.GetAttr();
+    if (!peer_ || peer_->PeerType() != BgpProto::EBGP)
+        return false;
+    if (!rhs.peer_ || rhs.peer_->PeerType() != BgpProto::EBGP)
+        return false;
+    return (attr_->neighbor_as() == rattr->neighbor_as());
+}
+
 BgpSecondaryPath::BgpSecondaryPath(const IPeer *peer, uint32_t path_id,
         PathSource src, const BgpAttrPtr ptr, uint32_t flags, uint32_t label)
     : BgpPath(peer, path_id, src, ptr, flags, label) {

src/bgp/bgp_path.h

@@ -123,6 +123,7 @@ class BgpPath : public Path {
 
     // Select one path over other
     int PathCompare(const BgpPath &rhs, bool allow_ecmp) const;
+    bool PathSameNeighborAs(const BgpPath &rhs) const;
 
 private:
     const IPeer *peer_;

src/bgp/routing-instance/rtarget_group_mgr.cc

@@ -118,6 +118,7 @@ void RTargetGroupMgr::BuildRTargetDistributionGraph(BgpTable *table,
         return;
     }
 
+    const BgpPath *best_ebgp_path = NULL;
     for (Route::PathList::iterator it = rt->GetPathList().begin();
          it != rt->GetPathList().end(); it++) {
         BgpPath *path = static_cast<BgpPath *>(it.operator->());
@@ -127,6 +128,14 @@ void RTargetGroupMgr::BuildRTargetDistributionGraph(BgpTable *table,
             continue;
 
         const BgpPeer *peer = static_cast<const BgpPeer *>(path->GetPeer());
+        if (peer->PeerType() == BgpProto::EBGP) {
+            if (!best_ebgp_path) {
+                best_ebgp_path = path;
+            } else if (!best_ebgp_path->PathSameNeighborAs(*path)) {
+                continue;
+            }
+        }
+
         std::pair<RtGroup::InterestedPeerList::iterator, bool> ret =
             peer_list.insert(std::pair<const BgpPeer *,
                  RtGroup::RTargetRouteList>(peer, RtGroup::RTargetRouteList()));

src/bgp/test/bgp_xmpp_rtarget_test.cc

@@ -3366,6 +3366,36 @@ TEST_F(BgpXmppRTargetTest, PathSelection5) {
     DeleteInetRoute(mx_.get(), NULL, "blue", BuildPrefix());
 }
 
+//
+// If RTargetRoute is received from EBGP peers in different ASes, VPN routes
+// should be sent to peers in AS of the best EBGP path.
+//
+TEST_F(BgpXmppRTargetTest, PathSelection6) {
+    Unconfigure();
+    task_util::WaitForIdle();
+    Configure(64496, 64497, 64498);
+    agent_a_1_->Subscribe("blue", 1);
+
+    AddRouteTarget(cn1_.get(), "blue", "target:1:1001");
+    AddRouteTarget(cn2_.get(), "blue", "target:1:1001");
+    task_util::WaitForIdle();
+
+    RTargetRoute *rtgt_rt =
+        VerifyRTargetRouteExists(mx_.get(), "64496:target:1:1001");
+    TASK_UTIL_EXPECT_EQ(2, rtgt_rt->count());
+    VerifyRTargetRouteNoExists(mx_.get(), "64497:target:1:1001");
+
+    AddInetRoute(mx_.get(), NULL, "blue", BuildPrefix());
+
+    BgpRoute *inet_rt =
+        VerifyInetRouteExists(cn1_.get(), "blue", BuildPrefix());
+    usleep(50000);
+    TASK_UTIL_EXPECT_EQ(1, inet_rt->count());
+    VerifyInetRouteNoExists(cn2_.get(), "blue", BuildPrefix());
+
+    DeleteInetRoute(mx_.get(), NULL, "blue", BuildPrefix());
+}
+
 //
 // Local AS is different than the global AS.
 // Verify that RTarget route prefixes use local AS while the route target