When a multicast network is divided into multiple PIM-SM domains, MSDP is required to connect Rendezvous Points (RPs) in different domains and enable RPs to share multicast source information. As a result, hosts in the local PIM-SM domain can receive multicast data sent by multicast sources in other domains.
On a multicast network that has multiple PIM-SM domains, to enable hosts in a local PIM-SM domain to receive multicast data from multicast sources in other domains, configure MSDP to connect RPs in different domains and enable RPs to share multicast source information.
To prevent Source Active (SA) messages from being blocked by Reverse Path Forwarding (RPF) rules and to reduce redundant traffic, performing the following operations is recommended:
Add all MSDP peers in the same autonomous system (AS) to the same mesh group.
Perform one of the following operations on the inter-AS MSDP peers:
Configure BGP to advertise routes, specify MSDP peers as routes' next hops, and configure advertised BGP routes to be preferentially selected by multicast devices.
Specify the RPs as static RPF peers of each other.
Add all inter-AS MSDP peers to the same mesh group. (This operation is recommended.)
Before configuring PIM-SM inter-domain multicast, complete the following tasks:
Configure a unicast routing protocol to ensure that unicast routes are reachable.
Enable multicast routing on all routers and PIM-SM on all router interfaces.
Divide the network into multiple PIM-SM domains and configure RPs.