Foundry Networks Switch and Router Installation And Configuration Manual page 656

Foundry Switch and Router Installation and Configuration Guide
Configuring Multicast Source Discovery Protocol (MSDP)
The Multicast Source Discovery Protocol (MSDP) is used by Protocol Independent Multicast (PIM) Sparse routers
to exchange routing information for PIM Sparse multicast groups across PIM Sparse domains. Routers running
MSDP can discover PIM Sparse sources that are in other PIM Sparse domains.
PIM Sparse routers use MSDP to register PIM Sparse multicast sources in a domain with the Rendezvous Point
(RP) for that domain.
Figure 18.4 shows an example of some PIM Sparse domains. For simplicity, this example show only one
Designated Router (DR), one group source, and one receiver for the group. Only one PIM Sparse router within
each domain needs to run MSDP.
PIM Sparse Domain 1
Designated Router (DR)
Rendezvous Point (RP)
206.251.14.22
1. DR receives traffic from source
Source for Group
and registers source with RP.
232.1.0.95
PIM Sparse Domain 3
Rendezvous Point (RP)
Figure 18.4 PIM Sparse domains joined by MSDP routers
In this example, the source for PIM Sparse multicast group 232.0.1.95 is in PIM Sparse domain 1. The source
sends a packet for the group to its directly attached DR. The DR sends a Group Advertisement message for the
group to the domain's RP. The RP is configured for MSDP, which enables the RP to exchange source information
with other PIM Sparse domains by communicating with RPs in other domains that are running MSDP.
The RP sends the source information to each of its peers by sending a Source Active message. The message
contains the IP address of the source, the group address to which the source is sending, and the IP address of the
RP interface with its peer. In this example, the Source Active message contains the following information:
• Source address: 206.251.14.22
• Group address: 232.1.0.95
• RP address: 206.251.17.41
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2. RP sends SA message
through MSDP to its MSDP
peers in other PIM Sparse
domains.
206.251.17.41
Source Advertisement message
4. When SA caching is enabled,
the RP immediately responds to
Join messages from receivers.
Otherwise, the RP and receiver
must wait for the next SA message
for the group.
PIM Sparse Domain 2
Rendezvous Point (RP)
3. RP that receives the SA
floods the SA to all its MSDP
peers, except the one that sent
the SA.
PIM Sparse Domain 4
Receiver for Group
232.1.0.95
Rendezvous Point (RP)
December 2000