RIP, IGRP timers question

Unanswered Question
Aug 7th, 2007

Greetings,

I'm rereading my materials for CCNA, and I can't quite fully understand when does which timer start counting down on these protocols.. My searches for this topic always came up only with their values&light descriptions. Could anybody please explain (or post a good link of) this matter?

Thanks!

I have this problem too.
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milos.kajanovic Wed, 08/08/2007 - 00:22

hi hardiklodhia,

I've skimmed the text and it too provides only basic description of the timers..

Anyway, my theory is,

update timer-starts upon setting up rip

invalid timer-same as update, if route 6x

unheard, deemed as invalid

holddown timer-starts when triggered update

about unreachable route heard ?

flush timer-no idea when this starts counting

(as update=30? as route invalid?)

*Do i get it correctly that when router detects a route is unreachable (how? interface down?), it does "route poisoning"(gives it metric of 16) & uses triggered update broadcast?

*Another one, "poison reverse", what's that good for? Again, I didn't find sense in it's basic description..

Thanks for any help! :)

hardiklodhia Wed, 08/08/2007 - 01:15

hi,

UPDATE:Rate in seconds at which updates are sent. This is the fundamental timing parameter of the routing protocol. The default is 30 seconds.

INVALID:Interval of time in seconds after which a route is declared invalid; it should be at least three times the value of 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. The default is 180 seconds.

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. The default is 180 seconds.

FLUSH:Amount of time in seconds that must pass before the route is removed from the routing table; the interval specified should be greater than the invalid value. 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. The default is 240 seconds.

and also chack :http://cisco.com/en/US/tech/tk365/tk554/tsd_technology_support_sub-protocol_home.html

hope this will help

rgrds,

milos.kajanovic Thu, 08/09/2007 - 16:39

Big Thanks hardiklodhia!

The link is also fairly nice, learned a couple of things&bookmarked it for later use :)

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