Dell PowerConnect B-RX Configuration Manual page 703

FIGURE 93
Designated Router (DR)
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, but 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:
•
•
•
Figure 93
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.
BigIron RX Series Configuration Guide
53-1002253-01
PIM Sparse domains joined by MSDP routers
PIM Sparse Domain 1
Rendezvous Point (RP)
206.251.17.41
206.251.14.22
Source for
1. DR receives traffic from source
Group
and registers source with RP.
232.1.0.95
PIM Sparse Domain 3
Rendezvous Point (RP)
Source address: 206.251.14.22
Group address: 232.1.0.95
RP address: 206.251.17.41
shows only one peer for the MSDP router (which is also the RP here) in domain 1, so the
Configuring Multicast Source Discovery Protocol (MSDP)
2. RP sends SA message
through MSDP to its MSDP
peers in other PIM Sparse
domains.
Source Advertisement message
4. 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)
23
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