Users Guide

Multicast Source Discovery Protocol (MSDP)
This chapter describes how to configure and use the multicast source discovery protocol (MSDP).
Protocol Overview
MSDP is a Layer 3 protocol that connects IPv4 protocol-independent multicast-sparse mode (PIM-SM) domains. A domain in
the context of MSDP is a contiguous set of routers operating PIM within a common boundary defined by an exterior gateway
protocol, such as border gateway protocol (BGP).
Each rendezvous point (RP) peers with every other RP via the transmission control protocol (TCP). Through this connection,
peers advertise the sources in their domain.
1. When an RP in a PIM-SM domain receives a PIM register message from a source, it sends a source-active (SA) message to
MSDP peers, as shown in the following illustration.
2. Each MSDP peer receives and forwards the message to its peers away from the originating RP.
3. When an MSDP peer receives an SA message, it determines if there are any group members within the domain interested
in any of the advertised sources. If there are, the receiving RP sends a join message to the originating RP, creating a
shortest path tree (SPT) to the source.
Figure 81. Multicast Source Discovery Protocol (MSDP)
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