Share-Mdt-Based Deliver Of Multicast Protocol Packets - 3Com MSR 50 Series Configuration Manual

Share-MDT-Based
Deliver of Multicast
Protocol Packets
Share-MDT establishment in a PIM-DM network
Figure 373 Share-MDT establishment in a PIM-DM network
IBGP: 11 .1 .3.1/24
PE 1
IBGP: 11.1.1.1/24
As shown in Figure 373, PIM-DM is running in the public network. The share-MDT
establishment is as follows: PE 1 initiates a flood-prune process in the entire public
network, with the IBGP interface address as the multicast source address, and the
share-group address as the multicast group address, of which all the other PE
devices that are running VPN instance A (PE 2 and PE 3) are group members, so
that a (11.1.1.1, 239.1.1.1) state entry is created on each device along the path in
the public network. This forms an SPT with PE 1 as the root, and PE 2 and PE 3 as
leaves. The flood-prune process initiated by PE 2 and PE 3 is similar. Finally, three
independent SPTs are established in the MD.
In the PIM-DM network, these independent SPTs constitute a share-MDT.
Characteristics of a share-MDT
As discussed above, a share-MDT is characterized as follows, no matter what PIM
mode is running in the public network:
All PE devices that support this VPN instance (PE 1, PE 2, and PE 3 in this
■
example) join the share-MDT.
All VPN multicast packets that belong to this VPN, including protocol packets
■
and data packets, are forwarded along the share-MDT to every PE device in the
public network, even if they have no active receivers downstream.
Where a multicast source and the receivers are located in different sites of a VPN,
multicast protocol packets must be transmitted across the public network.
Protocol packets are encapsulated into normal multicast data packets for the
public network on the local PE device, transmitted along the share-MDT, and then
decapsulated on the remote PE device to go into the normal protocol procedure.
Finally a distribution tree is established across the public network.
PE 3
P
PE 2
MD
IBGP : 11.1.2.1/24
How MD-VPN Works
Share-Group: 239.1.1.1
Public instance IBGP peers
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)
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