Dell Configuration Guide for the S4048–ON System 9.14.2.5

On each VLAN where the VLT peer nodes act as the first hop or last hop routers, one of the VLT peer nodes is elected as the PIM designated router. If you configured IGMP snooping along with PIM on the VLT VLANs, you must configure VLTi as the static multicast router port on both VLT peer switches. This ensures that for first hop routers, the packets from the source are redirected to the designated router (DR) if they are incorrectly hashed. In addition to being first-hop or last -hop routers, the peer node can also act as an intermediate router.

On a VLT-enabled PIM router, if any PIM neighbor is reachable through a Spanned Layer 3 (L3) VLAN interface, this must be the only PIM-enabled interface to reach that neighbor. A Spanned L3 VLAN is any L3 VLAN configured on both peers in a VLT domain. This does not apply to server-side L2 VLT ports because they do not connect to any PIM routers. These VLT ports can be members of multiple PIM-enabled L3 VLANs for compatibility with IGMP.

To route traffic to and from the multicast source and receiver, enable PIM on the L3 side connected to the PIM router using the ip pim sparse-mode command.

Each VLT peer runs its own PIM protocol independently of other VLT peers. To ensure the PIM protocol states or multicast routing information base (MRIB) on the VLT peers are synced, if the incoming interface (IIF) and outgoing interface (OIF) are Spanned, the multicast route table is synced between the VLT peers.

To verify the PIM neighbors on the VLT VLAN and on the multicast port, use the show ip pim neighbor, show ip igmp snooping mrouter, and show running config commands.

You can configure virtual link trunking (VLT) peer nodes as rendezvous points (RPs) in a Protocol Independent Multicast (PIM) domain.

If the VLT node elected as the designated router fails and you enable VLT Multicast Routing, multicast routes are synced to the other peer for traffic forwarding to ensure minimal traffic loss. If you did not enable VLT Multicast Routing, traffic loss occurs until the other VLT peer is selected as the DR.