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http://www.cisco.com/en/US/tech/tk828/tech_brief09186a00800a4415.html

Anycast RP—Logical RP

A very useful application of MSDP is called Anycast RP. This is a technique for configuring a multicast Sparse Mode network to provide for fault tolerance and load sharing within a single multicast domain.

Two or more RPs are configured with the same IP address on loopback interfaces, say 10.0.0.1 for example (refer to Figure 13). The loopback address should be configured as a 32 bit address. All the downstream routers are configured so that they know that their local RP's address is 10.0.0.1. IP routing automatically selects the topologically closest RP for each source and receiver. Since some sources might end up using one RP, and some receivers a different RP there needs to be some way for the RPs to exchange information about active sources. This is done with MSDP. All the RPs are configured to be MSDP peers of each other. Each RP will know about the active sources in the other RP's area. If any of the RPs was to fail, IP routing will converge and one of the RPs would become the active RP in both areas.

Figure 13 Anycast RP