HP MSR2003 Configuration Manual page 149

As shown in
PIM-SM routers that assume different roles function differently.
MSDP peers created on RPs:
•
Source-side MSDP peer—MSDP peer nearest to the multicast source, such as RP 1. The
source-side RP creates and sends SA 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 cannot advertise
the multicast source information out of the PIM-SM domain.
Receiver-side MSDP peer—MSDP peer nearest to the receivers, typically the receiver-side RP,
such as RP 3. After receiving an SA message, the receiver-side MSDP peer resolves the multicast
source information carried in the message. Then, it joins the SPT rooted at the multicast source
across the PIM-SM domains. 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—MSDP peer with multiple remote MSDP peers, such as RP 2. An
intermediate MSDP peer forwards SA messages received from one remote MSDP peer to other
remote MSDP peers. It functions as a relay for forwarding multicast source information.
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 only
forward received SA messages.
In a PIM-SM network using the BSR mechanism, the RP is dynamically elected from C-RPs. A PIM-SM
network typically has multiple C-RPs to ensure network robustness. Because the RP election result is
unpredictable, MSDP peering relationships must be built among all C-RPs to always keep the winning
C-RP on the MSDP interconnection map. Losing C-RPs assume the role of common PIM-SM routers on this
map.
Inter-domain multicast delivery through MSDP
As shown in
the existence of Source through multicast source registration. RPs in PIM-SM 2 and PIM-SM 3 also seek
the location of Source so that multicast traffic from Source can be sent to their receivers. MSDP peering
relationships must be established between RP 1 and RP 3 and between RP 3 and RP 2.
Figure 48, an MSDP peer can be created on any PIM-SM router. MSDP peers created on
Figure 49, an active source (Source) exists in the domain PIM-SM 1, and RP 1 has learned
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