Configuring MTI Parameters

Context

A multicast tunnel interface (MTI) is the inbound/outbound interface of a multicast distribution tree (MDT) and is used for interaction between the public network instance and a VPN instance. A PE encapsulates VPN multicast packets in to public network multicast data packets by using the MTI address as the source address.

Perform the following steps on a PE.

Procedure

Configure an IP address for the MTI.
An MTI can be configured with a static IP address or obtain an IP address dynamically. If both methods are used, the manually configured IP address takes precedence. The dynamic IP addressing mode ensures that the MTI IP address is the same as the IP address for establishing an IBGP neighbor relationship. This prevents RPF check failures caused by inconsistency of the two IP addresses.
- Configuring the MTI to automatically obtain an IP address
  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 VPN instance IPv4 address family view is displayed.
  4. Run multicast-domain source-interface interface-type interface-number
    
    The source interface of the MTI is specified.
    
    The PE will use the IP address of the source interface as the source IP address to encapsulate VPN multicast data packets.
    
    The source interface must be the interface on which the public network IBGP neighbor relationship is established. If not, VPN multicast packets received on the MTI cannot pass RPF checks.
- Manually configuring an IP address for the MTI
  1. Run system-view
    
    The system view is displayed.
  2. Run interface mtunnel interface-number
    
    The MTI view is displayed.
    
    Set interface-number to the MTI created when the Share-Group is configured. Otherwise, a message will be displayed, indicating that the MTI has not been created.
  3. Run ip address ip-address { mask | mask-length }
    
    An IP address is configured for the MTI.
    
    The MTI address must be the same as that of the interface on which the public network IBGP neighbor relationship is established; otherwise, VPN multicast packets received on the MTI cannot pass RPF checks.
(Optional) Configure the MTU for the MTI.
1. Run system-view
  The system view is displayed.
2. Run interface mtunnel interface-number
  The MTI view is displayed.
3. Run mtu mtu
  The MTU is configured for the MTI.
  
  By default, the MTU of an MTI is 1472 bytes.
  
  If the length of a VPN multicast packet is equal or nearly equal to the MTU of the outbound interface of the public network instance, the length of GRE-encapsulated public network multicast data packet will exceed the MTU of the outbound interface. In this case, the local PE must fragment the encapsulated packet before sending it through the outbound interface. The remote PE needs to reassemble the packet.
  
  You can set a smaller MTU for the MTI so that VPN multicast packets can be fragmented before being encapsulated using GRE. In this case, the remote PE does not need to reassemble the packets, so the forwarding efficiency is improved.