Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

Anycast RP allows you to configure two or more RPs with the same IP address on Loopback interfaces. The Anycast RP Loopback address are configured with a 32-bit mask, making it a host address. All downstream routers are configured to know that the Anycast RP Loopback address is the IP address of their local RP. IP routing automatically selects the closest RP for each source and receiver. Assuming that the sources are evenly spaced around the network, an equal number of sources register with each RP. Consequently, all the RPs in the network share the process of registering the sources equally. Because a source may register with one RP and receivers may join to a different RP, a method is needed for the RPs to exchange information about active sources. This information exchange is done with MSDP.

With Anycast RP, all the RPs are configured to be MSDP peers of each other. When a source registers with one RP, an SA message is sent to the other RPs informing them that there is an active source for a particular multicast group. The result is that each RP is aware of the active sources in the area of the other RPs. If any of the RPs fail, IP routing converges and one of the RPs becomes the active RP in more than one area. New sources register with the backup RP. Receivers join toward the new RP and connectivity is maintained.