A PIM-SM network uses the Source-Specific Multicast (SSM) model to provide specified multicast services to user hosts. User hosts in a multicast group can receive multicast data sent to their group from the specified multicast source.
Before configuring PIM-SM in the SSM model, configure a unicast routing protocol to ensure that unicast routes on the network are reachable. Because multicast devices do not maintain unicast routing information independently on the network, the devices must perform the RPF check on the received packets according to the unicast routing information on the network before creating PIM routing entries.