Allied Telesis AR400 Robustness Variable, What this counter does, How to change this counter

Configurable IGMP timers and counters > Robustness Variable

Robustness Variable

What this counter does

The Robustness Variable (RV) allows you to tune for the expected packet loss on a subnet. If you expect a subnet to be lossy, you can increase the RV. IGMP is robust to packet loss of one packet less than the RV. The RV is an integer from 1 to 5 and should not be set to 1.

If packet loss or lag time is an issue in your network, we recommend increasing the Robustness Variable on the Snoopers and the Querier. This increases the following:

zthe number of Queries that the Querier sends out (by increasing the LMQC)

zthe amount of time that the Querier and the Snoopers wait for clients to reply

For more details, see "Consequences for high-loss and high-lag networks" on page 60.

Potential problems with changing this counter

The RV is the counter you are most likely to need to change. However, you need to appreciate the effect this has on your network, as described in RFC 2236. Changing the RV changes other values from the RFC, as follows:

zLast Member Query Count = Robustness Variable

zDefault Timeout Interval = (Robustness Variable * Default Query Interval) + one Query Response Interval in seconds

Since software versions 281-03 and 2.9.1, the Default Timeout Interval automatically changes to match the above formula. For earlier versions, you must change it yourself, as described on page 82.

zStartup Query Count = Robustness Variable

zOther Querier Timeout = (Robustness Variable * Default Query Interval) + (Query Response Interval in seconds/2)

How to change this counter

The following example changes RV to 5, which is suitable for an extremely lossy network. Note that the Last Member Query Count and Default Timeout Interval also change.

Manager Switch 1> set ip igmp robustness=5

Info (1005003): Operation successful.

Manager Switch 1> show ip igmp

IGMP Protocol

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

Status	Enabled
Default Query Interval	125	secs
Default Timeout Interval	635	secs
Last Member Query Interval	10 (1/10secs)
Last Member Query Count	5
Robustness Variable	5
Query Response Interval	100	(1/10secs)
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Page 75 AlliedWare™ OS How To Note: IGMP