4000 Router Series IP Multicast Configuration Guide

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Default-MDT establishment

The multicast routing protocol running on the public network can be PIM-DM or PIM-SM. The process of

creating a default-MDT is different in these PIM modes.

Default-MDT establishment in a PIM-DM network

Figure 60 Default-MDT establishment in a PIM-DM network

As shown in Figure 60, PIM-DM is enabled in the network and all the PE devices support VPN instance

A. The process of establishing a default-MDT is as follows:

1. To establish PIM neighboring relationships with PE 2 and PE 3 through the MTI in VPN instance A,

PE 1 encapsulates the PIM protocol packet of the private network into a public network multicast

data packet by specifying the source address as the IP address of the MD source interface and the

multicast group address as the default-group address, and then send it to the public network.

With other PE devices that support VPN instance A as default-group members, PE 1 of VPN

instance A initiates a flood-prune process in the entire public network and a (11.1.1.1, 239.1.1.1)

state entry is created on each device along the path on the public network. This forms an SPT with

PE 1 as the root, and PE 2 and PE 3 as leaves.

2. At the same time, PE 2 and PE 3 separately initiate a similar flood-prune process.

Finally, three independent SPTs are established in the MD, constituting a default-MDT in the

PIM-DM network.