If I dont change any timers for RIP ( both v1 & v2) .. the hold down time is merely 20-30 sec.. The prefix for which a poisioned route is recevied is instantly deleted from routing table and it shows "possible down" in rip database for some seconds and also gets removed from RIP database after 2 -3 poisoned updates . However I expect the route to be atleast 180/240 sec in RIP database. Also if in between ( less than 180 sec) a good route is learnt it gets instantly placed in routing table.
Then why do we say that hold down is normally 180 and flush time is 240 sec..
are you referring to the regular (30 seconds interval) updates that RIP sends ? The holddown and flush timers are only applicable if NO update is received. The updates sent are applied immediately...
'If a router does not receive an update from another router for 180 seconds or more, it marks the routes served by the nonupdating router as being unusable. If there is still no update after 240 seconds, the router removes all routing table entries for the nonupdating router'
The default hold down timer value is 180 seconds. That is, a route is supposed to stay in hold down state for 180 seconds but with the following two exceptions:
1. Flush timer is lower than the sum of invalid+hold down timer. Then the route is cleared even before the hold down timer expires. Default invalid+holdtimer is 180+180=360 and the flush timer is 240 seconds, which means in less than 60 seconds into the hold down timer status the route gets purged. The timing may slightly differ (can be anywhere from 30-60 seconds) in this seconds depending on when the last inaccessible route update was received.
2. If the same prefix is learnt with a better metric then the route in hold down state is removed immediately to accodomate the new route.
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