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MD-VPN overview
The basic concepts involved in MD-VPN are described in
Table 19
Basic concepts in MD-VPN
Concept Description
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 between all PE devices in the
same VPN. MDT types include share-MDT and switch-MDT.
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 MD. An MTI
handles only multicast packets but not unicast packets. An MTI is
automatically created with the configuration of a share-group and
MTI binding for a VPN instance.
Share-group
In the public network, each MD is assigned an independent multicast
address, called share-group. A share-group is the unique identifier of
an MD on the public network. It helps build a share-MDT
corresponding to the MD on the public network.
Share-multicast distribution tree
(Share-MDT)
A share-MDT is an MDT that uses a share-group as its group address.
In a VPN, the share-MDT is uniquely identified by the share-group. A
share-MDT is automatically created after configuration and will
always exist on the public network, regardless of the presence of any
actual multicast services on the public network or the VPN.
Switch-multicast distribution tree
(Switch-MDT)
A switch-MDT is an MDT that uses a switch-group as it group address.
At MDT switchover, PE devices with receivers downstream join a
switch-group, forming a switch-MDT, along which the ingress PE
forwards the encapsulated VPN multicast traffic over the public
network.
Switch-group
When the multicast traffic of a VPN reaches or exceeds a threshold,
the ingress PE device assigns it an independent multicast address
called switch-group, and notifies the other PE devices that they should
use that address to forward the multicast traffic for that VPN. This
initiates a switchover to the switch-MDT.
Switch-group-pool
The switch-group-pool is a range of multicast addresses. At MDT
switchover, an address (namely, switch-group address) is chosen
from the switch-group-pool. The multicast packets for the VPN that
enter the public network at the PE device will be encapsulated using
that address. The switch-group-pool of a VPN must not overlap that of
another VPN, and must not contain the share-group of another 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.
