3Com 8807 Configuration Manual page 474

474 C 45: MSDP C
HAPTER
Working Principle
ONFIGURATION
Identifying multicast source and receiving multicast data
As shown in Figure 114, the RPs of PIM-SM domains 1, 2 and 3 establish peer
relationship between them. Domain 3 contains a group member.
Figure 114 MSDP working principles (I)
Group
Member
RP&MSDP Peer
PIM-SM 2
When the multicast source in domain 1 sends data to the multicast group, the
working process of the member in domain 3, from discovering the multicast
source to receiving data from the source, includes the following:
The multicast source in PIM-SM domain 1 begins to send datagram.
The DR connected to the multicast source encapsulates the datagram into a
Register packet and forward to the RP in domain 1.
The RP in domain 1 decapsulates the packet and forwards it along the RPT to all
the members within the domain. The domain members can choose to take the
path along SPT.
The RP in domain 1 generates an SA (Source Active) message for the MSDP peers
(the RPs in PIM-SM domain 2 and domain 3). The SA message contains multicast
source IP address, multicast group address and the address of the RP that
generates the message. Besides, the RP in domain 1 encapsulates the first received
multicast data into this SA message.
If there is any group member in the domain of an MSDP peer (in the figure, it is
PIM-SM domain 3), the RP in this domain sends the multicast data encapsulated in
the SA message to group members along the RPT and the join message to
multicast source.
After the reverse forwarding path is created, the multicast source data is sent
directly to the RP in domain 3, which then RP forwards the data along the RPT. In
this case, the last hop router connected with the group member in domain 3 can
choose whether to switch to SPT.
PIM-SM 1
DR
1
2
Register
3
Source
RP&MSDP Peer
4
4
4
5
RP&MSDP Peer
5
Group
Member
PIM-SM 3