Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Software Configuration Guide, Release 12.2(33)MRB
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Appendix B Cisco MWR 2941 Router Command Reference
ip igmp query-interval
If a lower version IGMP-enabled interface (that is, an interface running IGMPv1 or v2) receives a higher
version IGMP query (IGMPv3) with a different query interval, the following events occur:
• An error message in the following format is displayed:
%IGMP-3-QUERY_INT_MISMATCH: Received a non-matching query interval <interval in
seconds>, from querier address <ip-address>
• If the query interval on the lower version IGMP-enabled interface has not been modified, the default
query interval appears under its respective interface configuration.
• If the query interval on the IGMP-enabled interface has been modified, the configured query interval
is updated to show the configured query interval under its respective interface configuration.
Note The show ip igmp interface command displays both the configured query interval and the received
query interval in its output.
Be careful when increasing the query interval in an environment with IGMPv2 routers (the default) and
Layer 2 (L2) snooping switches: An IGMPv2 snooping switch needs to know the query interval of the
IGMP querier, because it is not signaled in IGMP messages (in IGMPv3 it is). The IGMP snooping
switch times out membership state based on what it thinks the query interval is. If the querier uses a
query interval larger than what the IGMP snooping switch assumes, then this may lead to an unexpected
timeout of multicast state on the IGMP snooping switch.
Note The default IGMP query interval on Cisco routers of 60 seconds is never an issue with Cisco IGMP
snooping switches because they either assume a 60 second-interval or tries to determine the query
interval by measuring the interval between IGMP general queries.
Be careful decreasing the query interval because it increases the processing load on the router (total
number of IGMP reports received over a period of time)—especially on routers with a large number of
interfaces and hosts connected to it (for example, a broadband aggregation router).
If the IGMP query interval and IGMP querier timeout period are modified on an interface, the following
conditions apply:
• By default, if the query interval is modified using the ip igmp query-interval command, the timeout
period automatically adjusts to two times the query interval; the adjusted timeout period, however,
is not be reflected in the interface configuration.
– To confirm that the timeout period adjusted to two times the modified query interval, you can
use the show ip igmp interface command; the output for this command displays the IGMP
query interval and timeout period being used for the interface.
– If you would like to have the ability to view the modified IGMP querier timeout period in the
interface configuration, you can manually configure the timeout period using the ip igmp
querier-timeout command. For the seconds argument, specify a value that is two times the
modified query interval.
• If the timeout period is modified using the ip igmp querier-timeout command, the query interval
does not automatically adjust to be in proportion with the modified timeout period (half of the
timeout period), so it is possible to override the default timeout period of two times the query
interval.
Note If the timeout period is modified for the ip igmp querier-timeout command, we recommend
that it be changed in proportion to the IGMP query interval.