Confusion in RIP timers

[pankaj kumar]

Hi

I have a confusion in the RIP timers please make me correct if i am wrong.

I think that if a router is does not  receive a update for a duration of 30 + 180(invalid time)  seconds it will make the route as invalid.

And after waiting for another 180 second for holddown time to expire.Means total time elapse is 390 sec (30 + 180(invalid timer) + 180(hold down time) ).

After the hold down time expires the router will wait for another 240 sec (flush time ) to remove the entry so total of 630 second.

[daniel.dib · Accepted solution]

The holddown timer is used to stabilize the network. When a route enters holddown, it can't be installed even if there is a new route with a better metric.

The default timers are 30 180 180 240 where 30 is the update timer, 180 for invalid and 180 for holddown and 240 for flush. The holddown timer is not part of the RFC.

After no updates for 180 seconds the route becomes invalid, the holddown timer starts at this time. 240 seconds from the last update the route is flushed. So the holddown timer never finishes because it would have to run for 360 seconds before leaving holddown, 180 + 180. The only way to test behavior of holddown is to set timers to something different. So with the timers basic command you could set it to 10 30 30 180. The route would become invalid after 30 seconds and and enter holddown, after 30 more it could leave holddown. If nothing happens for 180 seconds in total the route will be flushed.

Daniel Dib
CCIE #37149

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[pankaj kumar]

so can we say that the flush down timer and hold time start simultaneously and they start as soon as invalid timer finishes.

if for these values

10 30 30 180

the flush time and hold time start simultaneously after 40 second and the route will be deleted after 180 second total of 220 seconds

and

hold time finishes after 30 sec from the time it starts means after 10 + 30 ( invalid time ) +30 ( hold time )

flush time finishes after 180 sec from the time it starts means after 10 + 30 (invalid time ) +180

[daniel.dib]

No,

The flush is based on the last received update. So after 180 seconds it will flush. It does not start when route becomes invalid.

Holddown starts when the route becomes invalid which happens after 30 seconds in that case. Invalid is also based on last update. So you have 30 seconds and then 30 seconds for hold, that is 60 seconds total.

Daniel Dib
CCIE #37149

Please rate helpful posts.

[pankaj kumar]

ok ,

suppose that we have received last update at 00:00:12 am

and the timers are 10 30 30 180

now the invalid time will start at 00:00:12 and the entry will be invalid at 00:00:42

and the hold time start at 00:00:42  till  00:01:12

and flush time start at 00:00:12 am

and the entry will be deleted at 00:03:12 am (00:00:12 + 180 seconds)

now it is correct??

[daniel.dib]

Yes, now you got it

Daniel Dib
CCIE #37149

Please rate helpful posts.

[vishaw jasrotia]

Very Good explanation Daniel....

[morialpesh008]

Hi Denial,

      First of all thanks for such a classical explanation,

You said that holddown timer is not a part of RFC, then which timer have RFC for RIP2? and what are their timers?

Also why cisco introduced holddown timer?

Alpesh

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