3Com 5500-SI Configuration Manual page 588

588 C 31: MSDP C
HAPTER ONFIGURATION
Figure 171 Identifying the multicast source and receiving multicast data
Source
(1)
DR
PIM-SM 1
Flow
MSDP peers
The complete interoperation process between a multicast source S in the PIM-SM1
domain and receivers in the PIM-SM1 and PIM-SM4 domains is as follows:
1 The multicast source S in the PIM-SM1 domain begins to send data packets.
2 The designated router (DR) connected to the multicast source S encapsulates the
received data in a Register message, and then forwards the message to RP1 in the
PIM-SM1 domain.
3 RP1 in the PIM-SM1 domain decapsulates the Register message, and then forwards
the message to all the members in the domain along the RPT. The members in the
domain can select whether to switch to the SPT.
4 At the same time, RP1 in the PIM-SM1 domain creates an SA message and sends the
message to the corresponding MSDP peers (RPs in the PIM-SM2 and PIM-SM3
domains). Finally, the SA message is forwarded to the RP in the PIM-SM4 domain. The
SA message contains the IP address of the multicast source, the multicast group
address, the address of the RP that has generate the SA message, and the first
multicast data received by the RP in the PIM-SM1 domain.
5 If group members (namely, receivers) exists in the PIM-SM domains where MSDP
peers of RP1 reside, for example, if group members exist in the PIM-SM4 domain, RP4
decapsulates the multicast data in the SA message and distributes the multicast data
to receivers along the RPT. RP4 also sends a Join message to the multicast source S at
the same time.
6 To avoid SA loop, MSDP peers perform RPF check on the received SA message. After
the RPF path is established, the data from the multicast source S is directly sent to RP4
in the PIM-SM4 domain. Then RP4 forwards the data along the RPT within the
domain. Now the last-hop router of connected with group members in the PIM-SM4
domain selects whether to switch to the SPT.
Forwarding messages between MSDP peers and performing RPF check
To establish an MSDP peering relationship between routers, you have to create routes
between routers to for SA messages to travel.
Assume that three autonomous systems (AS) exist. They are AS1, AS2, and AS3. Each
AS has a PIM-SM domain associated with it. Each PIM-SM domain contains at least
one RP. See Figure 172.
RP2
(4)
RP1
(2)
(5)
(3)
user
PIM-SM 2
(4)
(5)
(4)
(4)
(4)
RP3
PIM-SM 3
user
(5)
RP4
PIM-SM 4