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CLI-based Configuration Guide - IP Multicast

AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R007

This document describes the principles and configurations of IP multicast, and provides configuration examples.
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IPv4 Multicast VPN Features Supported by the Device

IPv4 Multicast VPN Features Supported by the Device

The device supports multiple IPv4 multicast VPN features, including MD VPN (MD is short for multicast domain), BGP A-D multicast VPN (A-D is short for auto-discovery), and multicast VPN extranet.

Multicast VPN Implementation Modes

At present, multicast VPN can be implemented in MD or BGP A-D mode.

The greatest advantage of the MD mode is that only Provider Edges (PEs) are required to support multi-instance. Customer Edges (CEs) and Providers (Ps) do not need to be upgraded, and the existing protocol independent multicast (PIM) configurations on CEs and Ps do not need to be modified. The MD scheme is transparent to CEs and Ps. In MD mode, however, multicast VPN can only run on the public network tunnel based on the multicast distribution tree (MDT) in the PIM-ASM model (PIM-ASM is short for protocol independent multicast - any-source multicast).

The advantage of the BGP A-D mode is that peers in a multicast VPN can be discovered automatically. Multicast VPN services can run on the public network tunnel based on the MDT in the PIM-SSM model (PIM-SSM is short for protocol independent multicast - source-specific multicast).


Multicast VPN that is implemented in MD mode is called MD VPN.

In MD VPN implementation, PEs that belong to an MD join the same multicast group by having a VPN instance added to the group on each of them, and this group is called the Share-Group.

A Share-MDT, short for Share-Multicast Distribution Tree, is set up when a private network PIM instance joins the Share-Group on each of the PEs. The Share-MDT transmits PIM packets and data packets from a PE in the VPN to other PEs within the same VPN. The Share-MDT is regarded as a multicast tunnel (MT) within the MD and is uniquely identified by a Share-Group address.

VPN data is transparently transmitted through the MT over the public network. A multicast tunnel interface (MTI) is configured on each PE to seamlessly connect to the MT. A VPN instance only knows that private network data is sent out from an MTI and will be received by another MTI on the remote end. As virtual interfaces, MTIs transmit data between private networks and the public network.

If the VPN spans several autonomous systems (ASs), VPN sites in different ASs need to be connected. In MD VPN, there are two connection modes:

  • VPN instance-to-VPN instance connection

  • Multi-hop External BGP (EBGP) connection

BGP A-D Multicast VPN

BGP A-D multicast VPN also needs to set up a Share-MDT in a Share-Group. Different from MD VPN, BGP A-D multicast VPN does not require manual specification of peer addresses. This is because BGP can automatically discover peers using its A-D function. Therefore, BGP A-D multicast VPN can transmit multicast VPN services through public network tunnels based on the MDT in the PIM-SSM model.

Switch-MDT Switchover

When multicast packets are forwarded along the share-MDT in the public network, the packets are forwarded to all PEs in the same VPN instance, regardless of whether there is a receiver at the site to which a PE is connected to. This may lead to data flooding in the VPN if the VPN multicast data is transmitted at a high rate, which wastes the network bandwidth and increases the stress on PEs.

The device uses an optimized MD scheme. A switch-MDT is set up between the PEs connected to VPN receivers and the PE connected to a VPN source for the high-rate VPN multicast data flowing to the public network. The multicast data flow is then switched from the Share-MDT to the Switch-MDT so that multicast data can be transmitted on demand.

The conditions for a Switch-MDT switchover are configurable.

Multicast VPN Extranet

The following situations may exist in multicast VPN applications:
  • Two enterprises in different VPNs need to communicate with each other.

  • A service provider in one VPN needs to provide multicast services for users in other VPNs.

In these situations where multicast data needs to be transmitted between VPNs, multicast VPN extranet can be deployed to implement the transmission.

Multicast VPN extranet uses an MDT that is set up in MD or BGP A-D mode and has multicast routing policies configured on PEs to carry out multicast between VPNs.

Updated: 2019-06-12

Document ID: EDOC1000097181

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