R3102-R3103-HP 6600/HSR6600 Routers IP Multicast Configuration Guide

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VPN multicast traffic between the PE devices and the CE devices is transmitted on a
per-VPN-instance basis, but the public network multicast traffic between the PE devices and the P
devices is transmitted through the public network.
• Logically, an MD defines the transmission range of the multicast traffic of a specific VPN over the
public network. Physically, an MD identifies all the PE devices that support that VPN on the public
network. Different VPN instances correspond to different MDs.
As shown in Figure 61, the e
llipse area in the center of each VPN instance plane represents an MD,
which serves that particular VPN. All the VPN multicast traffic in that VPN is transmitted within that
MD.
• Inside an MD, all the private traffic is transmitted through the MT. The process of multicast traffic
transmission through an MT is as follows:
a. The local PE device encapsulates the VPN data into a public network packet.
b. Then, the PE device forwards the packet to the public network.
c. The remote PE device de-encapsulates the packet to turn it back into a private packet.
• The local PE device sends VPN data through the MTI, and the remote PE devices receive the private
data through the MTI.
As shown in Figure 61, you
can think of an MD as a private data transmission pool, and you can
regard an MTI as an entrance or exit of the pool. The local PE device puts the private data into the
transmission pool (the 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 any remote PE device that needs the data can get it from the respective exit (MTI).
Figure 61 Relationship between PIM on the public network and an MD in a VPN instance
• Each VPN instance is assigned a unique share-group address. The VPN data is transparent to the
public network.
A PE device encapsulates any VPN multicast packet within a normal public network multicast
packet, no matter what multicast group the VPN packet is destined for and whether it is a protocol
packet or a data packet. The PE device uses the share-group as the public network multicast group
for the packet. Then, the PE sends the public network multicast packet onto the public network.
• A share-group corresponds to a unique MD. For each share-group, a unique share-MDT is
constructed through the public network resources for multicast data forwarding. All the VPN