Service Manual

Table Of Contents
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
During failure cases, when a VLT node goes down and comes back up all the ND entries learned via VLT
interface must be synchronized to the peer VLT node
Synchronization of IPv6 ND Entries in a Non-VLT Domain
L3 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 L2 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.
In the present design the NDPM entries learned on non-VLT interfaces are synchronized with the peer
VLT nodes in case the ND entries are learned on spanned VLANs so that each node can do L3 forwarding
on behalf of each other. Whenever a VLAN is configured on 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 is synchronized to VLT
node2.
Tunneling of 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 top
of the rack (ToR) switch. The tunneled NA will carry some control information along with it so that the
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Virtual Link Trunking (VLT)