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How MSDP works
MSDP peers
Configuring one or more pairs of MSDP peers in the network forms an MSDP interconnection map,
where the RPs of different PIM-SM domains are interconnected in series. An SA message that an RP sends
and that these MSDP peers relay can be delivered to all other RPs.
Figure 58 Where MSDP peers are in the network
As shown in Figure 58, 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 include the following types:
{ 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 peer 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. After 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.
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