Command:

timers basic

Mode:

Router(config-router)#


Syntax:
timers basic update invalid holddown flush [sleeptime]

no timers basic


Syntax Description:

update

Rate in seconds at which updates are sent. This is the fundamental timing parameter of the routing protocol.

invalid

The passing of an interval of time in seconds which a route is declared invalid. It should be at least three times the value of the update. A route becomes invalid when there is an absence of updates that refresh the route. The route then enters holddown. The route is marked inaccessible and advertised as unreachable. However, the route is still used for forwarding packets.

holddown

Interval in seconds during which routing information regarding better paths is suppressed. It should be at least three times the value of update. A route enters into a holddown state when an update packet is received that indicates the route is unreachable. The route is marked inaccessible and advertised as unreachable. However, the route is still used for forwarding packets. When holddown expires, routes advertised by other sources are accepted and the route is no longer inaccessible.

flush

Amount of time in seconds that must pass before the route is removed from the routing table; the interval specified must be at least the sum of invalid and holddown. If it is less than this sum, the proper holddown interval cannot elapse, which results in a new route being accepted before the holddown interval expires.

sleeptime

(Optional) Interval in milliseconds for postponing routing updates in the event of a flash update. The sleeptime value should be less than the update time. If the sleeptime is greater than the update time, routing tables will become unsynchronized.


Command Description:

To adjust IGRP network timers, use the timers basic router configuration command. To restore the default timers, use the no form of this command.

The basic timing parameters for IGRP are adjustable. Since this routing protocol is executing a distributed, asynchronous routing algorithm, it is important that these timers be the same for all routers and access servers in the network.


Note    The current and default timer values can be seen by inspecting the output of the show ip protocols EXEC command. The relationships of the various timers should be preserved as described previously.

Example:

The following example sets updates to be broadcast every 5 seconds. If a router is not heard from in 15  seconds, the route is declared unusable. Further information is suppressed for an additional 15  seconds. At the end of the suppression period, the route is flushed from the routing table.

Router(config)#router igrp 109
Router(config-router)#timers basic 5  15  15  30

Note that by setting a short update period, you run the risk of congesting slow-speed serial lines; however, this is not a big concern on faster-speed Ethernets and T1-rate serial lines. Also, if you have many routes in your updates, you can cause the routers to spend an excessive amount of time processing updates.


Misconceptions:
None

Related commands:

 

None


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