HP 6125XLG Ip Multicast Configuration Manual page 181

An MD logically defines the transmission boundary of the multicast traffic of a specific VPN over the
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public network. It also physically identifies all the PE devices that support that VPN instance on the
public network. Different VPN instances correspond to different MDs.
As shown in Figure
that provides services for a particular VPN instance. 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
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transmission through an MT is as follows:
a. The local PE device encapsulates a VPN multicast packet into a public network multicast
packet.
b. The encapsulated multicast packet is sent by the PE device and travels over the public network.
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. The remote PE devices receive the private data
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from their MTI interfaces.
As shown in Figure
an entrance or exit of the pool. The local PE device puts the private data into the transmission pool
(MD) through the entrance (MTI). The transmission pool automatically duplicates the private data
and transmits the data to each exit (MTI) of the transmission pool. 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
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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. The default-group address is used 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
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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, regardless of which
PE device they used to enter the public network.
57, the ellipse area in the center of each VPN instance plane represents an MD
58, you can think of an MD as a private data transmission pool and an MTI as
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