HP MSR2000/3000/4000 Router Series IP Multicast Configuration Guide

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c. After receiving the multicast packet, the remote PE device decapsulates the multicast packet to
get the original VPN multicast packet.
• The local PE device sends VPN data out of the MTI, and the remote PE devices receive the private
data from their MTI interfaces.
As shown in Figure 58, you
can think of an MD as a private data transmission pool and an MTI as
an entrance or exit of the pool. The local PE device puts the private data into the transmission pool
(MD) through the entrance (MTI), and the transmission pool automatically duplicates the private
data and transmits the data to each exit (MTI) of the transmission pool, so that a remote PE device
that needs the data can get it from its exit (MTI).
Figure 58 Relationship between PIM on the public network and an MD in a VPN instance
• Each VPN instance is assigned a unique default-group address. The VPN data is transparent to the
public network.
A PE device encapsulates a VPN multicast packet (a multicast protocol packet or a multicast data
packet) into a public network multicast packet, specifying the default-group address as the public
network multicast group. Then, the PE sends this multicast packet to the public network.
• A default-group corresponds to a unique MD. For each default-group, a unique default-MDT is
constructed through the public network resources for multicast data forwarding. All the VPN
multicast packets transmitted in this VPN are forwarded along this default-MDT, no matter through
which PE device they entered the public network.
NOTE:
A
VPN uniquely corresponds to an MD and an MD provides services for only one VPN, which is called a
one-to-one relationship. Such a relationship exists between VPN, MD, MTI, and default-group.