rip timer

Hi,

I was playing around with a RIP enabled lab, and a question popped up, I couldnt answer by looking at any material I had or searching the web including the technology handbook from Cisco.

Update timer, specifies how often RIP should update.. Check.
Invalid timer, specifies the timer that ticks down after the latest update. If it is reached, the route becomes invalid. Check.
Holddown timer, specifies for how long the router should "not listen" to other non-better routes to a network. Check.

The flush timer is what gets me. In my lab, when the invalid timer is up. it sends out a poison update (hop count 16) to everyone, and it marks it as possibly down (invalid), but why not flush it right there and then, why wait an additional "flush-timer" before flushing it from the routing table, since its only the router itself that has that route now.

Same goes for IGRP ofcourse.

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Comments

scheistermeister

In case the link comes back up. Forgot to mention that they also look for a better route during that time.

kpjungle

scheistermeister wrote:

In case the link comes back up. Forgot to mention that they also look for a better route during that time.

But if the link that was down comes back up, wont the router with the link sent out an update specifying the link in its update packet?

Update: It would seem the only reason the flush timer is there, is to make sure the router has enough time to send out advertisements that the route is dead.