Users Guide

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 VLT nodes. VLT V6 VLAN and neighbor discovery protocol monitor (NDPM) entries
synchronization between VLT nodes is performed.
The VLT V6 VLAN information must synchronize 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 scenarios:
• When you enable and configure VLT on both VLT node1 and node2, any dynamically learned ND entry
in VLT node1 be synchronizes instantaneously to VLT node2 and vice-versa. The link-local address also
synchronizes if learned on the VLT VLAN interface.
• During failure cases, when a VLT node goes down and comes back up all the ND entries learned via VLT
interface must synchronize to the peer VLT node.
Synchronization of IPv6 ND Entries in a Non-
VLT Domain
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 Layer 2 access nodes. With ND synchronization, both the VLT
nodes perform Layer 3 forwarding on behalf of each other. Synchronization of NDPM entries learned on non-
VLT interfaces between the non-VLT nodes.
NDPM entries learned on non-VLT interfaces synchronize with the peer VLT nodes in case the ND entries are
learned on spanned VLANs so that each node can complete Layer 3 forwarding on behalf of each other.
Whenever you configure a VLAN on a VLT node, this information is communicated to the peer VLT node
regardless of whether the VLAN configured is a VLT or a non-VLT interface. If the VLAN operational state
(OSTATE) is up, dynamically learned ND entry in VLT node1 synchronizes to VLT node2.
Tunneling IPv6 ND in a VLT Domain
Tunneling an NA packet from one VLT node to its peer is required because an NA may reach the wrong VLT
node instead of arriving at the destined VLT node. This may occur because of LAG hashing at the ToR switch.
The tunneled NA carries some control information along with it so that the appropriate VLT node can mimic
the ingress port as the VLT interface rather than pointing to VLT node’s interconnecting link (ICL link).
Virtual Link Trunking (VLT) 1177