Static Multicast Routes

Static multicast routes are used to provide a parent multicast protocol like PIM (PIM) a different set of nexthops to use for the RPF (reverse-path-forwarding) checks.

When conducting an RPF check, these routes are examined first, and, if no nexthop is found, the unicast routing table is examined.

PIM (PIM) expects packets to arrive on the reverse-path forwarding (RPF) interface - the interface used to reach the source of the multicast data.

PIM also checks the RPF to learn which interface it should use to send join/prune messages.

By default, PIM checks the unicast routing table to identify the RPF interface.

Static multicast routes provide an alternative route table to use for the RPF check.

If a static multicast route and a unicast route are available for a specific destination, PIM uses the static multicast route.

Static multicast routes let PIM be independent of unicast routing.

This lets you deploy topologies in which multicast and unicast traffic flow over different paths.

For example, in order to balance the traffic load, you can separate the HTTP traffic from the stock quotes traffic. You simply configure a static multicast route to the source network that specifies a next hop gateway address different from the next hop address (for the same source) in the unicast routing table.

Note - PIM is the only protocol that uses static multicast routes.