Configuring an MTI

Context

MTIs are virtual interfaces. MTIs allow interaction between the public network instance and VPN instances on PEs. By exchanging PIM packets between MTIs, PEs can set up PIM neighbor relationships with each other in the public network instance.

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

Automatic configuration mode

If a PE is bound to multiple VPN instances, each instance needs to be configured with an MTI address. In this situation, you can use automatic configuration to configure IP addresses for all MTIs globally.
Manual configuration mode

When the number of VPN instances bound to a PE is small, you can configure an IP address and a Maximum Transmission Unit (MTU) for each MTI manually.

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

Procedure

Configure the automatic configuration mode globally.
1. Run system-view
  The system view is displayed.
2. Run multicast-domain source-interface interface-type interface-number
  An interface from which an MTI references an IP address is specified for all VPN instances.
  
  To avoid frequent protocol changes caused by interface flapping, use the loopback interface address as the MTI address.
3. Run commit
  The configuration is committed.
Configure the automatic configuration mode for a specified VPN instance.
1. Run system-view
  The system view is displayed.
2. Run ip vpn-instance vpn-instance-name
  The VPN instance view is displayed.
3. Run ipv4-family
  The 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 for the VPN instance.
  
  To avoid frequent protocol changes caused by interface flapping, use the loopback interface address as the MTI address.
5. Run commit
  The configuration is committed.
Configure the manual configuration mode.
1. Run system-view
  The system view is displayed.
2. Run interface mtunnel number
  The MTI interface view is displayed.
  
  Before running the interface mtunnel number command, ensure that a Share-Group has been configured, and the specified MTI has been bound to it.
3. Run ip address ip-address { mask | mask-length }
  The IP 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 Border Gateway Protocol (IBGP) peer relationship on the PE on the public network. Otherwise, the multicast packets of private networks 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.
  
  When being transmitted between a VPN instance and the public network instance, multicast packets need to be encapsulated into or decapsulated from tunnels. If the length of multicast packets of private networks equals or approaches the maximum transmission unit (MTU) of the outbound interface of the public network instance, the length of packets into which multicast packets are encapsulated will exceed the MTU of the outbound interface of the public network instance. The encapsulated packets then need to be fragmented before being sent out through the outbound interface of the public network instance and reassembled after arriving at the receive end. Therefore, setting a small MTU on the MTI is recommended to allow large multicast packets of private networks to be fragmented before being encapsulated into packets. Packets then do not need to be reassembled on the receive end, and this improves efficiency.
5. Run commit
  The configuration is committed.