IP multicast routing

Multicast PIM routing provides fast failover. For each VSX downstream VLAN, both VSX switches as a PIM Designate Router (DR). One node is the actual DR, the other node is the proxy DR.

From the PIM protocol view point (join, prune, register. The role of the proxy DR is equal to the role of the actual DR. The proxy DR also sends IM join messages to the upstream PM router. Any VSX node receives a copy of IGMP join on the SL. Both the DR and proxy DR maintain the same multicast tables and build the shortest path tree.

The proxy DR does not route traffic to downstream nodes. The proxy DR only acts as a bridge, all mroute entries present in the DB for downstream VLA is being set as bridge entries in the proxy DR ASIC, for example pointing to the DR VSX node. Only the actual DR performs multicast routing and forward traffic destined to groups to its downstream VLANs in the data-path. There is no PIM asset mechanism as PIM forwarder is the DR.

DR/Proxy DR election is done per VLAN. Election process is first DR priority, then the highest IP address.

Multicast PIM routing is enabled through the active-active command. For example:
switch(config)# router pim
switch(config-pim)# active-active
See the Command-Line Interface Guide for your switch model and software version for more information about the active-active command.
IP multicast routing fast-failover