The Multicast Source Discovery Protocol (MSDP) protocol
is used to implement multicast routing and data forwarding between
PIM-SM domains and anycast Rendezvous Point (RP) in a PIM-SM domain.
This section describes how to set up an MSDP peer relationship between PIM-SM domains in an autonomous system (AS) and how to configure MSDP peers to implement PIM-SM inter-domain multicast.
Anycast RP indicates that when multiple RPs with the same address reside in the same PIM-SM domain and MSDP peer relationships are set up between these RPs, IP routing automatically selects the topologically closest RP for each source and receiver. In this manner, burdens on a single RP are released, RP backup is implemented, and the forwarding path is optimized.
MSDP peers should set up TCP connections. You can then flexibly control the sessions set up between MSDP peers by closing or re-establishing TCP connections. You can also adjust the interval for retrying to set up a TCP connection between MSDP peers.
An SA cache is used to save the (S, G) information carried in SA messages locally. When a device needs to receive multicast data, it directly obtains available (S, G) information from the SA cache.
If the capacity of the SA cache enabled on the remote MSDP peer is too large, configuring sending SA Request message on the local device can shorten the time taken by a receiver to obtain multicast source information. And you can configure filtering rules for receiving SA Request messages on a specified remote MSDP peer.
By default, an SA message carries only (S, G) information. Then, if burst multicast data need be transmitted between domains, you can configure multicast data encapsulation for an SA message on the source RP. In addition, you can set the TTL threshold to limit the transmission scope of multicast data encapsulated in an SA message.
By default, a device receives all SA messages that pass the RPF check, and forwards the SA messages to all MSDP peers. To control the transmission of SA messages among MSDP peers, you can configure rules to filter the constructing, receiving, and forwarding SA messages.
This describes how to check the running status of MSDP through commands. You can clear the statistics on MSDP peers and the (S, G) information cached in the SA cache, or enable the MSDP debugging function if necessary.
This section provides examples for implementing PIM-SM inter-domain multicast through MSDP and inter-AS multicast through static RPF peers as well as configuring anycast RP in a PIM-SM domain.