Allied Telesis AR400 manual Configurable IGMP timers and counters, Timer and counter relationships

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:

zLast Member Query Count = Robustness Variable

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

zStartup Query Count = Robustness Variable

The Startup Query Count is the number of General Queries that the Querier sends when it starts up.

zOther 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.

Page 69 AlliedWare™ OS How To Note: IGMP