3Com Switch 8800 Advanced Software V5 Configuration Guide

610 CHAPTER 43: MSDP CONFIGURATION
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■ MSDP is applicable only if the intra-domain multicast protocol is PIM-SM.
■ MSDP is meaningful only for the any-source multicast (ASM) model.
How MSDP Works MSDP peers
As shown in Figure 186, an active multicast source (Source) exists in the domain
PIM-SM 1, and RP 1 has learned the existence of Source through multicast source
registration. If receiver hosts in PIM-SM 2 and PIM-SM 3 also wish to receive
multicast data from Source, the RPs in these domains can learn the location of
Source by establishing MSDP peering relationships. MSDP peering relationships
can be established among RPs of different or the same PIM-SM domain, between
RPs and multicast routers, or even between multicast routers.
With one or more pairs of MSDP peers configured in the network, an MSDP
interconnection map is formed, where the RPs of different PIM-SM domains are
interconnected in series. Relayed by these MSDP peers, an SA message sent by an
RP can be delivered to RPs in other domains.
Figure 186 Where MSDP peers are in the network
The blue lines in Figure 186 interconnect MSDP peers. 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 in
Figure 186. 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
source-side RP, like RP 3 in
Figure 186. 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.
MSDP peers
RP 1
PIM-SM 1
Source
Router A
PIM-SM 2
Router B
RP 2
PIM-SM 3
RP 3
Receiver