3Com Switch 7750 Configuration Guide Guide

Overview 441
Figure 106 Typical networking of Anycast RP
Typically, a multicast source S registers with the nearest RP to create an SPT, and
receivers also send Join messages to the nearest RP to construct an RPT. Therefore,
it is likely that the RP with which the multicast source has registered is not the RP
that receivers join. To ensure information consistency between RPs, the RPs,
serving as MSDP peers of one another, learn information of the peer multicast
source by sending SA messages to one another. As a result, each RP can know all
the multicast sources in the PIM-SM domain. In this way, the receivers connected
to each RP can receive multicast data sent by all the multicast sources in the entire
PIM-SM domain.
As described above, RPs exchange information among one another through
MSDP, a multicast source registers with the nearest RP, and receivers join the
nearest RPT. In this way, RP load balancing can be achieved. When an RP fails, the
multicast source and receivers previously registered to/joined it will register to or
join another nearest RP automatically, thus implementing RP redundancy backup.
MSDP Working
Mechanism
Identifying a multicast source and receiving multicast data
A network contains four PIM-SM domains, PIM-SM1, PIM-SM2, PIM-SM3, and
PIM-SM4. An MSDP peering relationship is established between RPs in different
domains. Multicast group members exist in the PIM-SM1 and PIM-SM4 domains.
See
Figure 107.
RP1 RP2
SA
MSDP
user
user
S1
S2
user
PIM-SM
SA message
MSDP peers
user
user