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

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Table 7 Basic MD-VPN concepts
Conce
p
t Descri
p
tion
Multicast domain (MD)
An MD is a set of VPN instances running on PE devices that can send
multicast traffic to each other. Each MD uniquely corresponds to the
same set of VPN instances.
Multicast distribution tree (MDT)
An MDT is a multicast distribution tree constructed by all PE devices in
the same VPN.
Multicast tunnel (MT)
An MT is a tunnel that interconnects all PEs in an MD for delivering
VPN traffic within the MD.
Multicast tunnel interface (MTI)
An MTI is the entrance to or exit of an MT, equivalent to an entrance
to or exit of an MD. PE devices use the MTI to access the MT. An MTI
handles only multicast packets but not unicast packets. The MTI
interfaces are automatically created when the MD for the VPN
instance is created.
Default-group
On the public network, each MD is assigned a unique multicast
address, called a default-group. A default-group is the unique
identifier of an MD on the public network. It helps build the
default-MDT for an MD on the public network.
Each VPN instance is assigned a unique default-group address.
Default-multicast distribution tree
(Default-MDT)
A default-MDT uses a default-group address as its group address. In a
VPN, the default-MDT is uniquely identified by the default-group. A
default-MDT is automatically created after the default-group is
specified and will always exist on the public network, regardless of
the presence of any multicast services on the public network or the
VPN.
Introduction to MD-VPN
The main points in MD-VPN implementation are as follows:
• The public network of the service provider supports multicast:
{ The PE devices must support the public network and multiple VPN instances.
{ Each instance runs PIM independently.
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.
• An MD logically defines the transmission boundary of the multicast traffic of a specific VPN over the
public network and 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 57, the e
llipse area in the center of each VPN instance plane represents an MD
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
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.