Modifying the IGMP Last-Member Query Interval

The last-member query interval is the maximum amount of time between group-specific query messages, including those sent in response to leave-group messages. You can configure this interval to change the amount of time it takes a routing device to detect the loss of the last member of a group.

When the routing device that is serving as the querier receives a leave-group message from a host, the routing device sends multiple group-specific queries to the group being left. The querier sends a specific number of these queries, and it sends them at a specific interval. The number of queries sent is called the last-member query count. The interval at which the queries are sent is called the last-member query interval. Both settings are configurable, thus allowing you to adjust the leave latency. The IGMP leave latency is the time between a request to leave a multicast group and the receipt of the last byte of data for the multicast group.

The last-member query count * the last-member query interval equals the amount of time it takes a routing device to determine that the last member of a group has left the group and to stop forwarding group traffic.

The default last-member query interval is 1 second. You can configure a subsecond interval up to one digit to the right of the decimal point. The configurable range is 0.1 through 0.9, then in 1-second intervals 1 through 999,999.

To modify this interval:

Configure the time (in seconds) that the routing device waits for a report in response to a group-specific query.
[edit]user@host# edit protocols igmpuser@host# set query-last-member-interval 0.1
Verify the configuration by checking the IGMP Last Member Query Interval field in the output of the show igmp interfaces command.

Note: You can configure the last-member query count by configuring the robustness variable; the two are always equal.

Modifying the IGMP Last-Member Query Interval

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