3com S7906E Instruccion De Instalación

 

1-7 

This section describes the implementation principle of the MD-VPN technology, including establishment 

of a share-MDT, packet delivery over it, and implementation of multi-AS MD-VPN. 

For a VPN instance, multicast data transmission in the public network is transparent. The MTIs at the 

local PE device and the remote PE device form a channel for the seamless transmission of private 

network data over the public network. 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, the multicast data 

transmission process (the MDT transmission process) over the public network is very complicated. 

The multicast routing protocol running in the public network can be PIM-DM, PIM-SM, or PIM-SSM. The 

process of creating a share-MDT is different in these three PIM modes.  

Figure 1-5 Share-MDT establishment in a PIM-DM network 

 

 

 

As shown in 

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

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

The public instance on PE 1 initiates a flood-prune process in the entire public network, with the BGP 

interface address (namely the interface address used to establish the BGP peer) as the multicast 

source address and the share-group address as the multicast group address. All the other PE devices 

that are running VPN instance A 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.  

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

independent SPTs are established in the MD. In the PIM-DM network, these independent SPTs 

constitute a share-MDT.