Static multicast routes

Depending on the application environment, a static multicast route can change an RPF route or create 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. In this way, the router creates a transmission path for multicast traffic that is different from the transmission path for unicast traffic.

As shown in Figure 16, when no static multicast route is configured, Switch C's RPF neighbor on the path back to the source is Switch A. The multicast data from the source travels through Switch A to Switch C. You can configure a static multicast route on Router C and specify Router B as Router C's RPF neighbor on the path back to the source. The multicast data from the source will travel along the path: Switch A to Switch B and then to Switch C.

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 for a multicast source to create an RPF route. In this way, a multicast routing entry is created to guide multicast forwarding.

As shown in Figure 17, 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 Switch C and Switch D as follows:

• On Switch C, configure a static multicast route for the multicast source and specify Switch B as the RPF neighbor.

• On Switch D, configure a static multicast route for the multicast source and specify Switch C as the RPF neighbor.

	NOTE: A static multicast route takes effect only on the multicast router on which it is configured, and will not be advertised throughout the network or redistributed to other routers.