3Com MSR 50 Series Configuration Manual page 1286

1286 C 75: M
HAPTER ULTICAST
VPN C
ONFIGURATION
the MTI on the ingress PE device. All that is known to the VPN instance is that the
VPN data is sent out the MTI and then the remote site can receive the data
through the MTI. Actually, when the remote site receives the multicast data, the
data transmission has come through a complicated process, that is, the MDT
transmission process.
The multicast routing protocol running in the public network can be either
PIM-SM or PIM-DM. The process of creating a share-MDT is different in these two
PIM modes.
Share-MDT establishment in a PIM-SM network
Figure 372 Share-MDT establishment in a PIM-SM network
IBGP: 11 .1 .3.1/24
PE 1
IBGP: 11.1.1.1/24
As shown in Figure 372, the process of establishing a share-MDT in a PIM-SM
network is as follows:
1 The public instance on PE 1 initiates a join to the public network RP, with the
share-group address as the multicast group address in the join message, and a (*,
239.1.1.1) state entry is created on each device along the path in the public
network. The join process initiated by PE 2 and PE 3 is similar. Finally, an RPT is
established in the MD, with the public network RP as the root and PE 1, PE 2 and
PE 3 as leaves.
2 The public instance on PE 1 registers the multicast source with the public network
RP, with the IBGP interface address as the multicast source address and the
share-group address as the multicast group address in the register message, and a
(11.1.1.1, 239.1.1.1) state entry is created on each device along the path in the
public network. The register process initiated by PE 2 and PE 3 is similar. Finally,
three SPTs between the PE devices and the RP are established in the MD.
In the PIM-SM network, the RPT, namely the (*, 239.1.1.1) tree, and the three
independent SPTs constitute a share-MDT.
PE 3
RP
P
PE 2
MD
IBGP : 11.1.2.1/24
Share-Group: 239.1.1.1
Public instance IBGP peers
RPT (*, 239.1.1.1)
SPT (11.1.1.1, 239.1.1.1)
SPT (11.1.2.1, 239.1.1.1)
SPT (11.1.3.1, 239.1.1.1)