3Com Switch 7750 Configuration Guide

482 CHAPTER 48: MSDP CONFIGURATION
Figure 120 Where MSDP peers are in the network
As shown in Figure 120, an MSDP peer can be created on any PIM-SM router.
MSDP peers created on PIM-SM routers that assume different roles function
differently.
1 MSDP peers on RPs
■ Source-side MSDP peer: the MSDP peer nearest to the multicast source
(Source), typically the source-side RP, like RP 1. The source-side RP creates SA
messages and sends the messages to its remote MSDP peer to notify the MSDP
peer of the locally registered multicast source information. A source-side MSDP
must be created on the source-side RP; otherwise it will not be able to advertise
the multicast source information out of the PIM-SM domain.
■ Receiver-side MSDP peer: the MSDP peer nearest to the receivers, typically the
receiver-side RP, like RP 3. Upon receiving an SA message, the receiver-side
MSDP peer resolves the multicast source information carried in the message
and joins the SPT rooted at the source across the PIM-SM domain. When
multicast data from the multicast source arrives, the receiver-side MSDP peer
forwards the data to the receivers along the RPT.
■ Intermediate MSDP peer: an MSDP peer with multicast remote MSDP peers,
like RP 2. An intermediate MSDP peer forwards SA messages received from one
remote MSDP peer to other remote MSDP peers, functioning as a relay of
multicast source information.
2 MSDP peers created on common PIM-SM routers (other than RPs)
Router A and Router B are MSDP peers on common multicast routers. Such MSDP
peers just forward received SA messages.
n
An RP is dynamically elected from C-RPs. To enhance network robustness, a
PIM-SM network typically has more than one C-RP. As the RP election result is
unpredictable, MSDP peering relationships should be built among all C-RPs so that
the winner C-RP is always on the “MSDP interconnection map”, while loser C-RPs
will assume the role of common PIM-SM routers on the “MSDP interconnection
map”.
MSDP peers
RP 1
PIM-SM 1
Source
Router A
PIM-SM 2
Router B
RP 2
PIM-SM 3
RP 3
Receiver