674 CHAPTER 48: MSDP CONFIGURATION
interconnected in series. Relayed by these MSDP peers, an SA message sent by an
RP can be delivered to all other RPs.
Figure 199 Where MSDP peers are in the network
As shown in Figure 199, 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
2 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.
3 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.
4 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.
5 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
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