Advanced Configuration and Management Guide
PIM Sparse Domain 1 |
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Designated Router (DR) | Rendezvous Point (RP) | 2. RP sends SA message | |
through MSDP to its MSDP | |||
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| peers in other PIM Sparse | |
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| domains. | |
206.251.17.41
Source Advertisement message
206.251.14.22
Source for Group | 1. DR receives traffic from source |
232.1.0.95and registers source with RP.
PIM Sparse Domain 3
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.
Rendezvous Point (RP)
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)
Figure 9.4 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
Figure 9.4 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.
Peer Reverse Path Forwarding (RPF) Flooding
When the MSDP router (also the RP) in domain 2 receives the Source Active message from its peer in domain 1, the MSDP router in domain 2 forwards the message to all its other peers. The propagation process is sometimes called “peer Reverse Path Forwarding (RPF) flooding”. This term refers to the fact that the MSDP router uses its
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