Dell S3048-ON Configuration Manual page 943

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 a
non-VLT interface. When VLT node1 receives NA on a VLT interface, it learns the Host MAC address on the received interface. This learned
neighbor entry is synchronized to VLT node2 as it is learned on ICL. If VLT node2 receives a NA packet on non-VLT interface which is
destined 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 forwards
the 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 is
received over ICL without tunneling header.
Traffic Destined to VLT Nodes
Hosts can send traffic to one of the VLT nodes using a global IP or Link-Local address. When the host communicates with the VLT node
using LLA and traffic reaches the wrong peer due to LAG level hashing in the ToR, the wrong peer routes the packet to correct the VLT
node though the destination IP is LLA. Consider a case in which traffic destined for VLT node1 reaches VLT node1 on the VLT interface and
traffic 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 node2
receives a packet on a VLT interface which is destined to VLT node1, it routes the packet to VLT node1 instead of switching the packet
because 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 achieved
using switching egress object for peers LLA.
VLT host to North Bound traffic flow
One of the VLT peer is configured as the default gateway router on VLT hosts. If the VLT node receives Layer 3 traffic intended for the
other 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, the
VLT node resolves the next hop. There may be traffic loss during the neighbor resolution period.
North-Bound to VLT host traffic flow
When a VLT node receives traffic from the north intended for the VLT host, it completes neighbor entry lookup and routes traffic to the
VLT interface. If the VLT interface is not operationally up, the VLT node routes the traffic over ICL. If the neighbor entry is not present, the
VLT node resolves the destination. There may be traffic loss during the neighbor resolution period.
VLT host to Non-VLT host traffic flow
When VLT node receives traffic intended to non-VLT host, it routes the traffic over non-VLT interface. If the traffic intended to non-VLT
host reaches wrong VLT peer due to LAG hashing in ToR, the wrong VLT node will resolve the destination over ICL and routes the traffic
over 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 flow
When VLT node receives traffic from non-VLT host intended to VLT host, it routes the traffic to VLT interface. If VLT interface is not
operationally up VLT node will route the traffic over ICL.
Non-VLT host to North Bound traffic flow
When VLT node receives traffic from non-VLT host intended to north bound with DMAC as self MAC it routes traffic to next hop. When
VLT node receives traffic from non-VLT host intended to north bound with DMAC as peer MAC it will not forward the packet to VLT peer
instead it will route the traffic to north bound next hop.
North Bound to Non-VLT host traffic flow
When VLT node receives traffic from north bound intended to the non-VLT host, it does neighbor entry lookup and routes traffic to VLT
interface. If traffic reaches wrong VLT peer, it routes the traffic over ICL.
Virtual Link Trunking (VLT) 943