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MD-VPN overview
For more information about the concepts of Protocol Independent Multicast (PIM), bootstrap router
(BSR), candidate-BSR (C-BSR), rendezvous point (RP), designated forwarder (DF), candidate-RP
(C-RP), shortest path tree (SPT) and rendezvous point tree (RPT), see "
."
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 in the public network. It helps build a share-MDT
corresponding to the MD in 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 in the public network, regardless
of the presence of any actual multicast services in 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. 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. It also 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
Main points in the implementation of MD-VPN 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
