Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 1046

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. 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. 1046 Virtual Link Trunking (VLT)