Msdp - Avaya 8800 Planning And Engineering

• One group in the SSM range can have a single source for a given SSM group.
• You can have different sources for the same group in the SSM range (different channels) if
they are on different switches.
Two different devices in a network may want to receive data from a physically closer server
for the same group. Hence, receivers listen to different channels (still same group).
For more information about PIM-SSM scaling, see
page 172.

MSDP

Multicast Source Discovery Protocol (MSDP) allows rendezvous point (RP) routers to share
source information across Protocol Independent Multicast Sparse-Mode (PIM-SM) domains.
RP routers in different domains use MSDP to discover and distribute multicast sources for a
group.
MSDP-enabled RP routers establish MSDP peering relationships with MSDP peers in other
domains. The peering relationship occurs over a TCP connection. When a source registers
with the local RP, the RP sends out Source Active (SA) messages to all of its MSDP peers.
The Source Active message identifies the address of the source, the multicast group address,
and the address of the RP that originates the message.
Each MSDP peer that receives the SA floods it to all MSDP peers that are downstream from
the originating RP. To prevent loops, each receiving MSDP peer examines the BGP routing
table to determine which peer is the next hop towards the RP that originated the SA. This
peer is the Reverse Path Forwarding (RPF) peer. Each MSDP peer drops any SAs that are
received on interfaces other than the one connecting to the RPF peer.
MSDP is similar to BGP and in deployments it usually follows BGP peering.
When receivers in a domain belong to a multicast group whose source is in a remote domain,
the normal PIM-SM source-tree building mechanism delivers multicast data over an
interdomain distribution tree. However, with MSDP, group members continue to obtain source
information from their local RP. They are not directly dependent on the RPs in other domains.
The following figure shows an example MSDP network.
Planning and Engineering — Network Design
PIM-SM and PIM-SSM scalability
November 2010
MSDP
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