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Configuring IP Multicast Protocols
December 2005
© Foundry Networks, Inc.
19 - 33
Figure 19.4
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. By default, the IP address included in the RP address field of the SA message is the IP
address of the originating RP. An SA message can use the IP address of any interface on the originating RP.
(The interface is usually a loopback interface.)
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
Figure 19.4 shows only one peer for the MSDP router (which is also the RP here) in domain 1, so the Source
Active message goes to only that peer. When an MSDP router has multiple peers, it sends a Source Active
message to each of those peers. Each peer sends the Source Advertisement to its other MSDP peers. The RP
that receives the Source Active message also sends a Join message for the group if the RP that received the
message has receivers for the group.
PIM Sparse Domain 3
Receiver for
Group
232.1.0.95
PIM Sparse Domain 4
PIM Sparse Domain 2
Source for
Group
232.1.0.95
PIM Sparse Domain 1
Designated
Router (DR)
206.251.14.22
Source Advertisement message
1. DR receives traffic from source
and registers source with RP.
2. RP sends SA message
through MSDP to its MSDP
peers in other PIM Sparse
domains.
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.
3. RP that receives the SA
floods the SA to all its MSDP
peers, except the one that sent
the SA.
Rendezvous
Point (RP)
206.251.17.41
Rendezvous
Point (RP)
Rendezvous
Point (RP)
Rendezvous
Point (RP)
Summary of Contents for FastIron Edge Switch X424
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