From CCIE Study Wiki

Multicast Source Discovery Protocol or MSDP allows rendezvous points to share multicast group info.

Theory

MSDP info allows multiple RP's to be configured for redundancy purposes in an enterprise environment (see Anycast RP or for RP's in totally separate multicast domains to subscribe to each other's active groups. It was originally developed for ISPs so they didn't have to rely on a competitors RP for multicast routing.

With MSDP, a RP establishes a TCP peering sessions with RPs (or border routers leading to other domains).

• When a RP learns about a new multicast source, it encapsulates the first data packet in a source-active or SA message and sends it out to all of its peers.
• The RP peers, upon receiving the SA, do a (modified) RPF Check and then forwards the SA to it's own peers. The SA is eventually flooded to all of the MSDP RPs.
• If a peer has a receiver interested in the traffic (i.e. it has a (*, G) entry for the group), it creates a (S,G) entry for the source and joins the shortest path tree for the source.
• The peer then decapsulates the SA packet and forwards the multicast data to the receiver(s).

A MSDP peer will periodically send SAs that include all sources within the domain of the RP.

When configuring MSDP, at least two loopback address will normally need to be present. One will be the shared RP address, and the other will be used as the unique local address the RP will use for peering.

Commands

• ip pim rp-address rp-address [access-list] [override] (global) - Configures the PIM RP address for all (or just those specified) multicast groups.
• ip msdp peer {peer-name | peer-address} [connect-source interface-type interface-number] [remote-as as-number] (global) - Configures a MSDP peer.
• ip msdp originator-id loopback [interface] (global) - Tells a MSDP speaker that originates a SA message to use the IP address of the specified interface as the RP address in the SA message.

Default Settings

• Nothing listed yet

Verification

• Nothing listed yet

Troubleshooting, Tips, and Tricks

• Nothing listed yet

Online Resources

• Cisco IOS IP multicast configuration guide's configuring basic IP multicast section on multicast source discovery protocol.

• Configuring MSDP from CCIE the Beginning.

• CCIE to Be sets up basic MSDP.

• Router Ric takes us through setting up multicast source discovery.

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