Cisco Systems 78-11741-02 manual Configuring a Default Msdp Peer, IPC-484

Configuring Multicast Source Discovery Protocol

MSDP Configuration Task List

Configuring a Default MSDP Peer

An MSDP peer of the local router is probably a BGP peer also. However, if you do not want to have or cannot have a BGP peer, you could define a default MSDP peer from which to accept all SA messages. The default MSDP peer must be a previously configured MSDP peer. Configure a default MSDP peer when you are not BGP- or multiprotocol BGP-peering with an MSDP peer. If a single MSDP peer is configured, a router will always accept all SA messages sent to it from that peer.

Figure 79 illustrates a scenario where default MSDP peers might be used. In the figure, a customer that owns Router B is connected to the internet via two Internet service providers (ISPs), one that owns Router A and the other that owns Router C. They are not running BGP or MBGP between them. In order for the customer to learn about sources in the ISP domain or in other domains, Router B identifies Router A as its default MSDP peer. Router B advertises SA messages to both Router A and Router C, but accepts SA messages either from Router A only or Router C only. If Router A is first in the configuration file, it will be used if it is up and running. If Router A is not running, then and only then will Router B accept SA messages from Router C.

The ISP will also likely use a prefix list to define which prefixes it will accept from the customer router. The customer will define multiple default peers, each having one or more prefixes associated with it.

The customer has two ISPs to use. The customer defines both ISPs as default peers. As long as the first default peer identified in the configuration is up and running, it will be the default peer and the customer will accept all SA messages it receives from that peer.

Figure 79 Default MSDP Peer Scenario

Router C

Default MSDP peer

ISP C PIM domain

	SA
	SA	10.1.1.1
	SA
Router A		Router B
Default MSDP peer		Default MSDP peer
ISP A PIM domain		Customer PIM domain

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Router B advertises SAs to Router A and Router C, but uses only Router A or Router C to accept SA messages. If Router A is first in the configuration file, it will be used if it is up and running. If Router A is not running, then and only then will Router B accept SAs from Router C. This is the behavior without a prefix list.

Cisco IOS IP Configuration Guide

IPC-484