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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.
Non-VLT host to Non-VLT host traffic flow
When VLT node receives traffic from non-VLT host intended to the non-VLT host, it does neighbor entry lookup and routes
traffic over ICL interface. If traffic reaches wrong VLT peer, it routes the traffic over ICL.
Router Solicitation
When VLT node receives router Solicitation on VLT interface/non-VLT interface it consumes the packets and will send RA back
on the received interface.
VLT node will drop the RS message if it is received over ICL interface.
Router Advertisement
When VLT node receives router advertisement on VLT interface/non-VLT interface it consumes the packets.
VLT node will drop the RA message if it is received over ICL interface.
Upgrading from Releases That Do Not Support IPv6 Peer Routing
During an upgrade to Release 9.4(0.0) from earlier releases, VLT peers might contain different versions of FTOS. You must
upgrade both the VLT peers to Release 9.4(0.0) to leverage the benefits of IPv6 peer routing.
Station Movement
When a host moves from VLT interface to non-VLT interface or vice versa Neighbor entry is updated and synchronized to VLT
peer. When a host moves from non-VLT interface of VLT node1 to non-VLT interface of VLT node2 neighbor entry is updated
and synchronized to VLT peer.
Virtual Link Trunking (VLT)
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