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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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Configuring an MTI

Configuring an MTI

An MTI can send and receive multicast data only after being enabled with the multicast function.


Multicast Tunnel Interfaces (MTIs) are virtual interfaces. They enable interaction between the public network instance and VPN instances on PEs. Exchanging PIM packets between MTIs, PEs can set up PIM neighbor relationships with each other in the public network instance.

When being transmitted between a VPN instance and the public network instance, multicast packets need to be encapsulated into or decapsulated from Generic Routing Encapsulation (GRE) packets. If the length of VPN multicast packets equals or approaches the MTU of the outbound interface of the public network instance, the length of GRE packets into which multicast packets are encapsulated will exceed the MTU of the outbound interface of the public network instance. The GRE packets then need to be fragmented before being sent out through the outbound interface of the public network instance and assembled after arriving at the receive end. Therefore, setting a small MTU on the MTI is recommended to make large VPN multicast packets be fragmented before being encapsulated into GRE packets. GRE packets then do not need to be assembled on the receive end, and this improves efficiency.


An MTI can be configured in either of the following modes:

  • Automatic mode
  • Manual mode

If both of the modes are configured, the manual configuration takes precedence over the automatic configuration.


  • Automatic configuration
    1. Run:


      The system view is displayed.

    2. Run:

      ip vpn-instance vpn-instance-name

      The VPN instance view is displayed.

    3. Run:


      An IPv4 address family is enabled for the VPN instance and the VPN instance IPv4 address family view is displayed.

    4. Run:

      multicast-domain source-interface interface-type interface-number

      An interface from which an MTI references an IP address is specified.


      To avoid frequent protocol changes caused by interface flapping, use the loopback interface address as the MTI address.

  • Manual configuration
    1. Run:


      The system view is displayed.

    2. Run:

      interface mtunnel number

      The MTI interface view is displayed.

    3. Run:

      ip address ip-address { mask | mask-length }

      The address of the MTI is configured.


      The MTI address must be the same as the IP address that is used to set up the Internal BGP (IBGP) peer relationship on the PE in the public network. Otherwise, the VPN multicast packets received on the MTI cannot pass the Reverse Path Forwarding (RPF) check.

    4. (Optional) Run:

      mtu mti-mtu

      The MTU value of the MTI is configured.

      By default, the MTU value of the MTI is 1472 bytes.

Updated: 2019-06-12

Document ID: EDOC1000097181

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