Usages of static multicast routes
A static multicast route can change an RPF route or create an RPF route.
Changing an RPF route
Typically, the topology structure of a multicast network is the same as that of a unicast network, and multicast traffic follows the same transmission path as unicast traffic does. You can configure a static multicast route for a multicast source to change the RPF route. As a result, the device creates a transmission path for multicast traffic that is different from the transmission path for unicast traffic.
Figure 28: Changing an RPF route
As shown in Figure 28, when no static multicast route is configured, Device C's RPF neighbor on the path back to the source is Device A. The multicast data from the source travels through Device A to Device C. You can configure a static multicast route on Device C and specify Device B as Device C's RPF neighbor on the path back to the source. The multicast data from the source travels along the path: Device A to Device B and then to Device C.
Creating an RPF route
When a unicast route is blocked, multicast forwarding might be stopped due to lack of an RPF route. You can configure a static multicast route to create an RPF route. In this way, a multicast routing entry is created to guide multicast forwarding.
Figure 29: Creating an RPF route
As shown in Figure 29, the RIP domain and the OSPF domain are unicast isolated from each other. For the receiver hosts in the OSPF domain to receive multicast packets from the multicast source in the RIP domain, you must configure Device C and Device D as follows:
On Device C, configure a static multicast route for the multicast source and specify Device B as the RPF neighbor.
On Device D, configure a static multicast route for the multicast source and specify Device C as the RPF neighbor.