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Page 69 | AlliedWare™ OS How To Note: IGMP
Configurable IGMP timers and counters > Timer and counter relationships
Configurable IGMP timers and counters
This section looks at some of the timers and counters that control how often IGMP sends
queries and how quickly entries time out. First, it gives background information in the
following subsections:
z "Timer and counter relationships" on page 69
z "Software versions" on page 70
z "Initial configuration" on page 70
z "Default values" on page 72
Then it looks at each of the configurable timers and counters, in the following subsections:
z "Last Member Query Count and Last Member Query Interval" on page 72
z "Robustness Variable" on page 75
z "Default Query Interval" on page 76
z "Query Response Interval" on page 77
z "Default Timeout Interval" on page 78 (the Group Membership Interval of RFC 2236)
RFC 2236 also describes other counters and timers that this section does not describe,
because this section only describes the counters and timers that you can directly set. The
router or switch derives other counters and timers from the above subset.
Timer and counter relationships
The above timers and counters are related to each other and to others in RFC 2236 by the
following formulae:
z Last Member Query Count = Robustness Variable
z Default Timeout Interval = (Robustness Variable * Default Query Interval) +
one Query Response Interval in seconds
z Startup Query Count = Robustness Variable
The Startup Query Count is the number of General Queries that the Querier sends when
it starts up.
z Other Querier Timeout = (Robustness Variable * Default Query Interval) +
(Query Response Interval in seconds/2)
The Other Querier Timeout is the length of time that a potential Querier waits after
receiving a Query before it assumes that it should become the Querier.
These relationships mean you need to take care if you change timers or counters. "Example
of bad choices for timer values" on page 83 describes the consequences of a bad combination
of values.