Users Guide

IPv6 Peer Routing in VLT Domains
Overview
VLT enables the physical links between two devices that are called VLT nodes or peers, and within a VLT
domain, to be considered as a single logical link to external devices that are connected using LAG bundles to
both the VLT peers. This capability enables redundancy without the implementation of Spanning tree
protocol (STP), thereby providing a loop-free network with optimal bandwidth utilization.
IPv6 peer routing is supported on all the platforms that are compatible with IPv6 routing and support VLT.
This functionality performs the following operations:
• Forwarding control traffic to the correct VLT node when the control traffic reaches the wrong VLT node
due to hashing at the VLT LAG level on the ToR.
• Routing the data traffic which is destined to peer VLT node.
• Synchronizing neighbor entries learned on VLT VLAN interfaces between the primary and secondary
node.
• Synchronizing the IP address of VLT VLAN interfaces between the VLT primary node and secondary
node.
• Performing routing on behalf of peer VLT nodes for a configured time period when a peer VLT node
goes down.
When you configure Layer 3 VLT peer routing using the peer-routing command in VLT DOMAIN mode, it
applies for both IPv4 and IPv6 traffic in VLT domains. Layer 3 VLT provides a higher resiliency at the Layer 3
forwarding level. Routed VLT allows you to replace VRRP with routed VLT to route the traffic from the Layer 2
access nodes. With neighbor discovery (ND) synchronization, both the VLT nodes perform Layer 3 forwarding
on behalf of each other.
The neighbor entries are typically learned by a node using neighbor solicitation (NS) and ND messages. These
NS or neighbor advertisement (NA) messages can be either destined to the VLT node or to any nodes on the
same network as the VLT interface. These learned neighbor entries are propagated to another VLT node so
that the peer does not need to relearn the entries.
IPv6 Peer Routing
When you enable peer routing on VLT nodes, the MAC address of the peer VLT node is stored in the ternary
content addressable memory (TCAM) space table of a station. If the data traffic destined to a VLT node,
node1, reaches the other VLT node, node2, owing to LAG-level hashing in the ToR switch, it is routed instead
of forwarding the packet to node1. This processing occurs because of the match or hit for the entry in the
TCAM of the VLT node2.
Virtual Link Trunking (VLT) 1176