PIM-SMLT

IP multicast routing support with Split MultiLink Trunking (SMLT) builds a virtual switch that represents the two switches of the split multilink trunk core.

When switches use PIM in the core, they need to exchange protocol-related updates as part of the interswitch trunking (IST) protocol. IST hides the fact that the edge switch attaches to two physical switches.

PIM-SMLT can work in triangular, square, and full mesh configurations with Layer 3 IP multicast. However, PIM-SSM in square or full mesh SMLT topologies is not supported.

The following rules apply:

SMLT provides for fast failover in all cases, but does not provide a functionality similar to Routed SMLT (RSMLT).

Important

Important

You must enable square SMLT globally before you configure square or full-mesh configurations.

Traffic delay with PIM while restarting peer SMLT switches

If you restart peer SMLT switches, you can lose, or experience a delay in, PIM traffic. The local and remote SMLT links must be up to forward traffic. If a remote SMLT link is down, you can experience a traffic delay.

PIM uses a DR to forward data to receivers on a VLAN. If you restart the DR in an SMLT VLAN, you can lose data because of the following actions:

A workaround to this delay is to a configure the static RP router on the peer SMLT switches. This feature avoids the process of selecting an active RP router from the list of candidate RPs and dynamically learning about RPs through the BSR mechanism. After the DR comes back up, traffic resumes as soon as OSPF converges. This workaround reduces the traffic delay to approximately 15 to 65 seconds.