Consider a situation in which NA for VLT node1 reaches VLT node1 on a non-VLT interface and NA for VLT node1 reaches VLT node2 on anon-VLT interface. When VLT node1 receives NA on a VLT interface, it learns the Host MAC address on the received interface. This learnedneighbor entry is synchronized to VLT node2 as it is learned on ICL. If VLT node2 receives a NA packet on non-VLT interface which isdestined to VLT node1, node 2 lifts the NA packet to CPU using an ACL entry then it adds a tunnel header to the received NA and forwardsthe packet to VLT node1 over ICL. When VLT node1 received NA over ICL with tunnel header it learns the Host MAC address on the ICL.Host entries learned on ICL will not be synchronized to the VLT peer.If NA is intended for VLT peer and DIP is LLA of peer, it is lifted to CPU and tunneled to the peer. VLT nodes will drop NA packet, If NA isreceived over ICL without tunneling header.Traffic Destined to VLT NodesHosts can send traffic to one of the VLT nodes using a global IP or Link-Local address. When the host communicates with the VLT nodeusing LLA and traffic reaches the wrong peer due to LAG level hashing in the ToR, the wrong peer routes the packet to correct the VLTnode though the destination IP is LLA. Consider a case in which traffic destined for VLT node1 reaches VLT node1 on the VLT interface andtraffic destined for VLT node1 reaches VLT node2 due to LAG level hashing in the ToR.When VLT node1 receives traffic on VLT interface, it consumes the packets and process them based on the packet type. If VLT node2receives a packet on a VLT interface which is destined to VLT node1, it routes the packet to VLT node1 instead of switching the packetbecause the match that occurs for the neighbor entry in the TCAM table.If the destination IP address is peers' link-local advertisement (LLA), the wrong VLT peer switches the traffic over ICL. This is achievedusing switching egress object for peers LLA.VLT host to North Bound traffic flowOne of the VLT peer is configured as the default gateway router on VLT hosts. If the VLT node receives Layer 3 traffic intended for theother VLT peer, it routes the traffic to next hop instead of forwarding the traffic to the VLT peer. If the neighbor entry is not present, theVLT node resolves the next hop. There may be traffic loss during the neighbor resolution period.North-Bound to VLT host traffic flowWhen a VLT node receives traffic from the north intended for the VLT host, it completes neighbor entry lookup and routes traffic to theVLT interface. If the VLT interface is not operationally up, the VLT node routes the traffic over ICL. If the neighbor entry is not present, theVLT node resolves the destination. There may be traffic loss during the neighbor resolution period.VLT host to Non-VLT host traffic flowWhen VLT node receives traffic intended to non-VLT host, it routes the traffic over non-VLT interface. If the traffic intended to non-VLThost reaches wrong VLT peer due to LAG hashing in ToR, the wrong VLT node will resolve the destination over ICL and routes the trafficover ICL. When Correct VLT node receives this routed traffic over ICL it will switch traffic to non-VLT interface.Non-VLT host to VLT host traffic flowWhen VLT node receives traffic from non-VLT host intended to VLT host, it routes the traffic to VLT interface. If VLT interface is notoperationally up VLT node will route the traffic over ICL.Non-VLT host to North Bound traffic flowWhen VLT node receives traffic from non-VLT host intended to north bound with DMAC as self MAC it routes traffic to next hop. WhenVLT node receives traffic from non-VLT host intended to north bound with DMAC as peer MAC it will not forward the packet to VLT peerinstead it will route the traffic to north bound next hop.North Bound to Non-VLT host traffic flowWhen VLT node receives traffic from north bound intended to the non-VLT host, it does neighbor entry lookup and routes traffic to VLTinterface. If traffic reaches wrong VLT peer, it routes the traffic over ICL.Virtual Link Trunking (VLT) 1041
