Allied Telesis AR400 Query Response Interval, What this timer does, How to change this timer

Configurable IGMP timers and counters > Query Response Interval

Query Response Interval

What this timer does

The Query Response Interval determines the longest time clients can take to reply to a General Query. The Querier inserts the Query Response Interval into General Query messages. Clients randomly choose a time between 0 and the Query Response Interval at which to respond to a General Query. Increasing the Query Response Interval spreads IGMP messages over a longer time period, which reduces the burstiness of traffic on the network.

The Query Response Interval is also referred to as the Max Response Time in RFC 2236.

It may be useful to decrease the Query Response Interval if you are running EPSR or RSTP. Decreasing the Query Response Interval reduces the recovery time after a topology change. For more information, see "Query solicitation (rapid recovery from topology changes)" on page 26.

Potential problems with changing this timer

If your network has many multicast clients and you make the Query Response Interval too short, you may congest the Snoopers and Querier with too many Report messages in a short time.

If you change the Query Response Interval, the Default Timeout Interval also needs to change, so that clients have an appropriate amount of time to reply to the Query. Since software versions 281-03 and 2.9.1, this happens automatically. For earlier versions, you need to change it yourself as described on page 82.

How to change this timer

The Query Response Interval is an integer from 1 to 255 in units of 0.1 seconds, specified using the queryresponseinterval parameter. The default is 100 (10 seconds). The following example would return a modified Query Response Interval to its default value.

Manager Switch 1> set ip igmp queryresponseinterval=100

Info (1005003): Operation successful.

Manager Switch 1> show ip igmp

IGMP Protocol

------------------------------------------------------------------------

Status	Enabled
Default Query Interval	125	secs
Default Timeout Interval	260	secs
Last Member Query Interval	10 (1/10secs)
Last Member Query Count	2
Robustness Variable	2
Query Response Interval	100	(1/10secs)
.

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In this example, the Querier sends a General Query every 125 seconds. The General Query contains the Query Response Interval of 100, which tells clients that they have 10 seconds to reply to this General Query message.

Page 77 AlliedWare™ OS How To Note: IGMP