Service Manual

Peer routing for IPv6 packets in a VLT domain is supported. This mechanism of 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 the control traffic to correct VLT node when the control traffic reaches 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 the neighbor entries learned on VLT VLAN interfaces between VLT 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 by 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 enables you to replace VRRP with routed VLT to route the traffic
from Layer 2 access nodes. With neighbor discovery (ND) synchronization, both the VLT nodes will
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.
Working of IPv6 Peer Routing
When peer routing is enabled 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. This section contains the following topics that describe the
operations and benefits of IPv6 peer routing in VLT domains:
Synchronization of IPv6 ND Entries in a VLT Domain
Because the VLT nodes appear as a single unit, the ND entries learned via the VLT interface are expected
to be the same on both the VLT nodes. VLT V6 VLAN and neighbor discovery protocol monitor (NDPM)
entries synchronization between VLT nodes is performed.
The VLT-v6 VLAN information needs to be synchronized with peer VLT node. Therefore, both the VLT
nodes are aware of the VLT VLAN information associated with the peers. The CLI configuration and
dynamic state changes of VLT v6 VLANs are notified to peer VLT node. The ND entries are generally
learned by a node from Neighbor Advertisements (NA). ND entries synchronization should be happening
on the following two scenarios:
When VLT has been configured and enabled on both VLT node1 and node2, any dynamically learned ND
entry in VLT node1 should be synchronized instantaneously to VLT node2 and vice-versa. The link-local
address will also be synchronized if learned on VLT VLAN interface
Virtual Link Trunking (VLT)
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