Overview

MSDP is an inter-domain multicast solution that addresses the interconnection of PIM-SM domains. It discovers multicast source information in other PIM-SM domains.

In the basic PIM-SM mode, a multicast source registers only with the RP in the local PIM-SM domain, and the multicast source information in each domain is isolated. As a result, both of the following occur:

• The RP obtains the source information only within the local domain.

• A multicast distribution tree is built only within the local domain to deliver multicast data locally.

MSDP enables the RPs of different PIM-SM domains to share their multicast source information. The local RP can then join the SPT rooted at the multicast source across the PIM-SM domains. This allows multicast data to be transmitted among different domains.

With MSDP peer relationships established between appropriate routers in the network, the RPs of different PIM-SM domains are interconnected with one another. These MSDP peers exchange source active (SA) messages, so that the multicast source information is shared among these domains.

MSDP is applicable only if the intra-domain multicast protocol is PIM-SM. MSDP takes effect only for the ASM model.

For more information about the concepts of DR, BSR, C-BSR, RP, C-RP, SPT, and RPT mentioned in this document, see "Configuring PIM."