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 pim query-interval
Note In PIM version 2, PIM hello messages also contain a variety of options that allow PIM routers on the
network to learn about the capabilities of PIM neighbors. For more information about these capabilities,
see the show ip pim neighbor command page.
PIM neighbor discovery messages are used to determine which router on a network is acting as the
Designated Router (DR) for PIM sparse mode (PIM-SM) and Source Specific Multicast (SSM). The DR
is responsible for joining PIM-SM and SSM groups receiving multicast traffic from sources requested
by receivers (hosts). In addition, in PIM-SM, the DR is also responsible for registering local sources with
the RP. If the DR fails, a backup router becomes the DR and then forward traffic for local receivers and
register local sources.
The period argument is used to specify the PIM hello (query) interval. The interval determines the
frequency at which PIM hello (query) messages are sent.
Note When an interfaces enabled for PIM comes up, a PIM hello (query) message is sent immediately. In
some cases, the initial PIM hello (query) message may be lost
.If the first PIM hello (query) does not get
sent when an interface initially comes up, another is sent 3 seconds later regardless of the PIM hello
(query) interval to ensure that there are no initialization delays.
The configured PIM hello interval also determines the holdtime used by a PIM router. The Cisco IOS
software calculates the holdtime as follows:
3 * the interval specified for the period argument
By default, PIM routers announce the holdtime in PIM hello (query) messages.If the holdtime expires
and another router has not received another hello (query) message from this router, it times out the PIM
neighbor. If the timed out router was the DR, the timeout triggers DR election. By default, the
DR-failover interval occurs after 90 seconds (after the default holdtime expires for a DR). To reduce
DR-failover time in redundant networks, a lower value for the period argument can be configured on all
routers. The minimum DR-failover time that can be configured (in seconds) is 3 seconds (when the
period argument is set to 1 second). The DR-failover time can be reduced to less than 3 seconds if the
msecs keyword is specified. When the msecs keyword is used with the ip pim query-interval command,
the value specified for the period argument is interpreted as a value in milliseconds (instead of seconds).
By enabling a router to send PIM hello messages more often, this functionality allows the router to
discover unresponsive neighbors more quickly. As a result, the router can implement failover or
recovery procedures more efficiently
Note If IGMP Version 1 is being used on a network, then the DR is also the IGMP querier; if at least IGMP
version 2 is being used, then the router with the lowest IP address becomes the IGMP querier.
Examples The following example shows how to set the PIM hello interval to 45 seconds:
interface FastEthernet0/1
ip pim query-interval 45
The following example shows how to set the PIM hello interval to 100 milliseconds:
interface FastEthernet0/1
ip pim query-interval 100 msec