3Com Switch 8800 Advanced Software V5 Configuration Guide

MSTP Overview 611
■ Intermediate MSDP peer: an MSDP peer with multicast remote MSDP peers,
like RP 2 in
Figure 186. 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 multicast 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 looser C-RPs
will assume the role of command PIM-SM routers on the "MSDP interconnection
map".
Implementing inter-domain multicast delivery by leveraging MSDP peers
As shown in Figure 187, an active source (Source) exists in the domain PIM-SM 1,
and RP 1 has learned the existence of Source through multicast source
registration. If RPs in PIM-SM 2 and PIM-SM 3 also wish to know the specific
location of Source so that receiver hosts can receive multicast traffic originated
from it, MSDP peering relationships should be established between RP 1 and RP 3
and between RP 3 and RP 2 respectively.
Figure 187 MSDP peering relationships
The process if implementing inter-domain multicast delivery by leveraging MSDP
peers is as follows:
1 When the multicast source in PIM-SM 1 sends the first multicast packet to
multicast group G, DR 1 encapsulates the multicast data within a register message
RP 1
DR 1
Source
PIM-SM 1
PIM-SM 3
PIM-SM 2
PIM-SM 4
RP 3
RP 2
DR 2
MSDP peers
SA message
Join message
Multicast packets
Register message
Receiver