Version 4.1 - 1.7.b MSDP
This section is going to be short and sweet. Even in the R/S track there was not really a lot of emphasis on this. Basically this is scaling the multicast network.
The Cisco Documentation Configuring Multicast Source Discovery Protocol says:
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.
MSDP depends heavily on BGP or MBGP for interdomain operation. MBGP is Multiprotocol BGP - which uses extensions on BGP to carry multicast routes.
I really don't see them getting into the weeds on this. I guess the most important thing on that page would be the benefits of using MSDP.
MSDP has the following benefits:
- It breaks up the shared multicast distribution tree. You can make the shared tree local to your domain. Your local members join the local tree, and join messages for the shared tree never need to leave your domain.
- PIM-SM domains can rely on their own RPs only, thus decreasing reliance on RPs in another domain. This increases security because you can prevent your sources from being known outside your domain.
- Domains with only receivers can receive data without globally advertising group membership.
- Global source multicast routing table state is not required, thus saving on memory.
And that's probably all that needs to be said about MSDP.