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Figure 146. Example of PIM-Sparse Mode on VLT
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 allows multicast traffic that originates from the source that is
connected to the VLT ports to reach the PIM router which has downstream neighbors.
The VLT peer nodes can also act as normal PIM routers on Layer 3 ports and on VLANs that do not have any VLT port
members. In addition to being first-hop or last -hop routers, the peer node can also act as an intermediate router.
To route traffic to and from the multicast source and receiver that are connected to VLT ports, enable PIM-Sparse mode on the
VLANs to which the VLT ports belong using the ip pim sparse-mode command. If you configure IGMP snooping on these
VLANs, the VLTi must be configured as a static multicast router port on both VLT peers.
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 cannot configure VLT peer nodes as rendezvous points, but you can connect PIM routers to VLT ports.
If the VLT node elected as the designated router fails, traffic loss will occur until another VLT node is elected the designated
router.
Virtual Link Trunking (VLT)
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