Cisco Systems 78-11741-02 manual Configuring Multicast Source Discovery Protocol, How Msdp Works

Configuring Multicast Source Discovery Protocol

This chapter describes the Multicast Source Discovery Protocol (MSDP) feature. For a complete description of the MSDP commands in this chapter, refer to the “Multicast Source Discovery Protocol Commands” chapter of the Cisco IOS IP Command Reference, Volume 3 of 3: Multicast publication. To locate documentation of other commands in this chapter, use the command reference master index, or search online.

MSDP is a mechanism to connect multiple Protocol Independent Multicast sparse mode (PIM-SM) domains. MSDP allows multicast sources for a group to be known to all rendezvous points (RPs) in different domains. Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains. An RP runs MSDP over TCP to discover multicast sources in other domains.

An RP in a PIM-SM domain has an MSDP peering relationship with MSDP-enabled routers in another domain. The peering relationship occurs over a TCP connection, where primarily a list of sources sending to multicast groups is exchanged. The TCP connections between RPs are achieved by the underlying routing system. The receiving RP uses the source lists to establish a source path.

The purpose of this topology is to have domains discover multicast sources in other domains. If the multicast sources are of interest to a domain that has receivers, multicast data is delivered over the normal, source-tree building mechanism in PIM-SM.

MSDP is also used to announce sources sending to a group. These announcements must originate at the RP of the domain.

MSDP depends heavily on BGP or MBGP for interdomain operation. We recommend that you run MSDP in RPs in your domain that are RPs for sources sending to global groups to be announced to the internet.

To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the “Identifying Supported Platforms” section in the “Using Cisco IOS Software” chapter.

How MSDP Works

Figure 78 illustrates MSDP operating between two MSDP peers. PIM uses MSDP as the standard mechanism to register a source with the RP of a domain.

When MSDP is configured, the following sequence occurs. When the first data packet of a source is registered by the first hop router, that same data packet is decapsulated by the RP and forwarded down the shared tree. That packet is also reencapsulated in a Source-Active (SA) message that is immediately forwarded to all MSDP peers. The SA message identifies the source, the group the source is sending to,

Cisco IOS IP Configuration Guide

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