Configuring MSDP Basic Functions 487■ Redundancy backup between RPs: When an RP fails, the multicast sourcepreviously registered with it or the receivers previous joined it will register withor join another nearest RP, thus achieving redundancy backup between RPs.c CAUTION:■ Be sure to configure a 32-bit subnet mask (255.255.255.255) for the AnycastRP address, namely configure the Anycast RP address into a host address.■ An MSDP peer address must be different from the Anycast RP address.Protocols and Standards MSDP is documented in the following specifications:■ RFC 3618: Multicast Source Discovery Protocol (MSDP)■ RFC 3446: Anycast Rendezvous Point (RP) mechanism using ProtocolIndependent Multicast (PIM) and Multicast Source Discovery Protocol (MSDP)Configuring MSDPBasic FunctionsTo enable exchange of information from the multicast source S between twoPIM-SM domains, you need to establish MSDP peering relationships between RPsin these PIM-SM domains. In this way, the information from the multicast sourcecan be sent through SA messages between the MSDP peers, and the receivers inother PIM-SM domains can finally receive the multicast source information.A BGP or MBGP route is required between two routers that are MSDP peers toeach other. Through this route, the two routers can transfer SA messages betweenPIM-SM domains, so BGP peers are the basic for establishing MSDP peers.For an area containing only one MSDP peer, known as a stub area, the BGP orMBGP route is not compulsory. SA messages are transferred in a stub area throughthe static RPF peers. In addition, the use of static RPF peers can avoid RPF check onthe received SA messages, thus saving resources.Before configuring static RPF peers, you must create an MSDP peering connection.If you configure only one MSDP peer on a router, the MSDP peer will act as a staticRPF peer. If you configure multiple static RPF peers, you need to handle them byusing different rules according to whether the rp-policy keyword is used toconfigure the filtering policies.When configuring multiple static RPF peers for the same router, you must followthe following two configuration methods:■ In the case that all the peers use the rp-policy keyword: Multiple static RPFpeers function at the same time. RPs in SA messages are filtered based on theconfigured prefix list, and only the SA messages whose RP addresses pass thefiltering are received. If multiple static RPF peers using the same rp-policykeyword are configured, when any of the peers receives an SA message, it willforward the SA message to other peers.■ None of the peers use the rp-policy keyword: Based on the configuredsequence, only the first static RPF peer whose connection state is UP is active.All the SA messages from this peer will be received, while the SA messagesfrom other static RPF peers will be discarded. Once the active static RPF peerfails (because the configuration is removed or the connection is terminated),based on the configuration sequence, the subsequent first static RPF peer
