8. List of timers and default values
8. List of timers and default values
Most of these timers are configurable. If non-default settings are used, they MUST be consistent among all routers on a single link. Note that parentheses are used to group expressions to make the algebra clear.
8.1. Robustness Variable
The Robustness Variable allows tuning for the expected packet loss on a subnet. If a subnet is expected to be lossy, the Robustness Variable may be increased. IGMP is robust to (Robustness Variable-1) packet losses. The Robustness Variable MUST NOT be zero, and SHOULD NOT be one. Default: 2
8.2. Query Interval
The Query Interval is the interval between General Queries sent by the Querier. Default: 125 seconds.
By varying the [Query Interval], an administrator may tune the number of IGMP messages on the subnet; larger values cause IGMP Queries to be sent less often.
8.3. Query Response Interval
The Max Response Time inserted into the periodic General Queries. Default: 100 (10 seconds)
By varying the [Query Response Interval], an administrator may tune the burstiness of IGMP messages on the subnet; larger values make the traffic less bursty, as host responses are spread out over a larger interval. The number of seconds represented by the [Query Response Interval] must be less than the [Query Interval].
8.4. Group Membership Interval
The Group Membership Interval is the amount of time that must pass before a multicast router decides there are no more members of a group on a network. This value MUST be ((the Robustness Variable) times (the Query Interval)) plus (one Query Response Interval).
8.5. Other Querier Present Interval
The Other Querier Present Interval is the length of time that must pass before a multicast router decides that there is no longer another multicast router which should be the querier. This value MUST be ((the Robustness Variable) times (the Query Interval)) plus (one half of one Query Response Interval).
8.6. Startup Query Interval
The Startup Query Interval is the interval between General Queries sent by a Querier on startup. Default: 1/4 the Query Interval.
8.7. Startup Query Count
The Startup Query Count is the number of Queries sent out on startup, separated by the Startup Query Interval. Default: the Robustness Variable.
8.8. Last Member Query Interval
The Last Member Query Interval is the Max Response Time inserted into Group-Specific Queries sent in response to Leave Group messages, and is also the amount of time between Group-Specific Query messages. Default: 10 (1 second)
This value may be tuned to modify the "leave latency" of the network. A reduced value results in reduced time to detect the loss of the last member of a group.
8.9. Last Member Query Count
The Last Member Query Count is the number of Group-Specific Queries sent before the router assumes there are no local members. Default: the Robustness Variable.
8.10. Unsolicited Report Interval
The Unsolicited Report Interval is the time between repetitions of a host's initial report of membership in a group. Default: 10 seconds.
8.11. Version 1 Router Present Timeout
The Version 1 Router Present Timeout is how long a host must wait after hearing a Version 1 Query before it may send any IGMPv2 messages. Value: 400 seconds.