Users Guide

Consider an example in which NA for VLT node1 reaches VLT node1 on the VLT interface and NA for VLT
node1 reaches VLT node2 due to LAG level hashing in ToR. When VLT node1 receives NA on VLT interface, it
learns the Host MAC address on VLT interface. This learned neighbor entry is synchronized to VLT node2 as it
is learned on VLT interface of Node2. If VLT node2 receives a NA packet on 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 receives NA over ICL with tunnel header
it learns the Host MAC address on VLT port channel interface. This learned neighbor entry is synchronized to
VLT node2 as it is learned on VLT interface of Node2.
If NA is intended for a VLT peer and DIP is LLA of the peer, it is lifted to the CPU and tunneled to the peer. VLT
nodes drop the NA packet if the NA is received over ICL without a tunneling header.
Neighbor Solicitation from Non-VLT Hosts
Consider a sample scenario in which NS for VLT node1 IP reaches VLT node1 on a non-VLT interface and NS
for VLT node1 IP reaches VLT node2 on a non-VLT interface. When VLT node1 receives NS from a non-VLT
interface, it unicasts the NA packet on the received interface. When NS reaches VLT node2, it floods on all
interfaces including ICL. When VLT node 1 receives NS on the ICL, it floods the NA packet on the VLAN. If NS
is unicast and if it reaches the wrong VLT peer, it is lifted to the CPU using the ACL entry. Then the wrong
peer adds a tunnel header and forwards the packet over the ICL.
Neighbor Advertisement from Non-VLT Hosts
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
Virtual Link Trunking (VLT) 1180