[MuxOrch] FDB ageout safety check (sonic-net#1674)

* FDB ageout extra check
* VS test to cover fdb ageout scenario

Author: prsunny

orchagent/muxorch.cpp

@@ -904,6 +904,14 @@ bool MuxOrch::isNeighborActive(const IpAddress& nbr, const MacAddress& mac, stri
         return ptr->isActive();
     }
 
+    NextHopKey nh_key = NextHopKey(nbr, alias);
+    string curr_port = getNexthopMuxName(nh_key);
+    if (port.empty() && !curr_port.empty() && isMuxExists(curr_port))
+    {
+        MuxCable* ptr = getMuxCable(curr_port);
+        return ptr->isActive();
+    }
+
     return true;
 }
 
@@ -1004,6 +1012,16 @@ void MuxOrch::updateNeighbor(const NeighborUpdate& update)
     {
         /* Check if the neighbor already exists */
         old_port = getNexthopMuxName(update.entry);
+
+        /* if new port from FDB is empty or same as existing port, return and
+         * no further handling is required
+         */
+        if (port.empty() || old_port == port)
+        {
+            addNexthop(update.entry, old_port);
+            return;
+        }
+
         addNexthop(update.entry);
     }
     else

tests/test_mux.py

@@ -169,6 +169,13 @@ def add_fdb(self, dvs, port, mac):
 
         time.sleep(1)
 
+    def del_fdb(self, dvs, mac):
+
+        appdb = dvs.get_app_db()
+        ps = swsscommon.ProducerStateTable(appdb.db_connection, "FDB_TABLE")
+        ps._del("Vlan1000:"+mac)
+
+        time.sleep(1)
 
     def create_and_test_neighbor(self, confdb, appdb, asicdb, dvs, dvs_route):
 
@@ -247,6 +254,23 @@ def create_and_test_fdb(self, appdb, asicdb, dvs, dvs_route):
         dvs_route.check_asicdb_deleted_route_entries([ip_2+self.IPV6_MASK])
         self.check_neigh_in_asic_db(asicdb, ip_2, 4)
 
+        # Simulate FDB aging out test case
+        ip_3 = "192.168.0.200"
+
+        self.add_neighbor(dvs, ip_3, "00:00:00:00:00:12")
+
+        # ip_3 is added to standby mux
+        dvs_route.check_asicdb_route_entries([ip_3+self.IPV4_MASK])
+
+        # Simulate FDB age out
+        self.del_fdb(dvs, "00-00-00-00-00-12")
+
+        # FDB ageout is not expected to change existing state of neighbor
+        dvs_route.check_asicdb_route_entries([ip_3+self.IPV4_MASK])
+
+        # Change to active
+        self.set_mux_state(appdb, "Ethernet4", "active")
+        dvs_route.check_asicdb_deleted_route_entries([ip_3+self.IPV4_MASK])
 
     def create_and_test_route(self, appdb, asicdb, dvs, dvs_route):