Technical Documentation

Enabling Multicast Snooping for Multichassis Link Aggregation Group Interfaces

Include the multichassis-lag-replicate-state statement at the [edit multicast-snooping-options] hierarchy level to enable IGMP snooping and state replication for multichassis link aggregation group (MC-LAG) interfaces.

multicast-snooping-options { multichassis-lag-replicate-state;}

Replicating join and leave messages between links of a dual-link MC-LAG interface enables faster recovery of membership information for MC-LAG interfaces that experience service interruption.

Without state replication, if a dual-link MC-LAG interface experiences a service interruption (for example, if an active link switches to standby) the membership information for the interface is recovered by generating an IGMP query to the network. This method can take from 1 through 10 seconds to complete, which may be too long for some applications.

When state replication is provided for MC-LAG interfaces, IGMP join or leave messages received on an MC-LAG device are replicated from the active MC-LAG link to the standby link through an Interchassis Communication Protocol (ICCP) connection. The standby link processes the messages as if they were received from the corresponding active MC-LAG link, except it does not add itself as a next hop and it does not flood the message to the network. After a failover, the multicast membership status of the link can be recovered within a few seconds or less by retrieving the replicated messages.

This example enables state replication for MC-LAG interfaces in a bridge domain named bridge1:

  1. Enable state replication for MC-LAG interfaces:
    user@host# set bridge-domains bridge1 multicast-snooping-options multicast-lag-replicate-state
  2. After you commit the configuration, multicast snooping automatically identifies the active link during initialization or after failover, and replicates data between the active and standby links without any administrator intervention.
  3. You can use the show igmp snooping interface command to display the state for MC-LAG interfaces:
    user@host> show igmp snooping interfaceInstance: bridge-domain bridge1 Learning-Domain: default Interface: ae0.1 State: Up Groups: 1 mc-lag state: standby Immediate leave: Off Router interface: no Interface: ge-0/1/3.100State: Up Groups: 1 Immediate leave: Off Router interface: no Interface: ae1.2State: Up Groups: 1 mc-lag state: standby Immediate leave: Off Router interface: no

    Note: You can use the show igmp snooping membership command to display group membership information for the links of MC-LAG interfaces.

  4. If you delete the multicast-lag-replicate-state statement or the configuration of IGMP snooping, replication between MC-LAG links stops within the hierarchy level from which the configuration was deleted. Then, multicast membership is recovered as needed by generating standard IGMP queries over the network.

Published: 2010-04-16