Best way to see this is to lab it up. I set up a very simple network with
R1 and R2 connected via ethernet. I advertised a loopback from R2 into RIP,
and then on R2 set the ethernet interface passive to stop routing updates
without giving IOS any hints by dropping the interface. Here's what
happened:
R1#sh ip ro | b Gate
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 2 subnets
R 10.1.0.0 [120/1] via 10.1.124.2, 00:00:12, FastEthernet0/0
C 10.1.124.0 is directly connected, FastEthernet0/0
R1#sh clock
22:03:17.475 UTC Wed Jan 19 2011
R1#!This is when I set Fa0/0 passive on R2
R1#
Jan 19 22:05:56.975: RIP-DB: invalidated route of 10.1.0.0/24 via 10.1.124.2
Jan 19 22:05:56.979: RT: delete route to 10.1.0.0 via 10.1.124.2, rip
metric [120/1]
Jan 19 22:05:56.979: RT: no routes to 10.1.0.0, entering holddown
Jan 19 22:05:56.987: RIP-DB: Remove 10.1.0.0/24, (metric 4294967295) via
10.1.124.2, FastEthernet0/0
R1#sh ip ro | b Gate
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 2 subnets
R 10.1.0.0/24 is possibly down,
routing via 10.1.124.2, FastEthernet0/0
C 10.1.124.0 is directly connected, FastEthernet0/0
R1#
Jan 19 22:06:56.991: RIP-DB: garbage collect 10.1.0.0/24
Jan 19 22:06:56.995: RT: delete subnet route to 10.1.0.0/24
R1#sh ip ro | b Gate
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.124.0 is directly connected, FastEthernet0/0
So 3 minutes after the last received update, the route was marked invalid,
and 60 seconds after that the route was flushed. So all timers are running
concurrently, the update timer, the invalid/holddown timers, and the flush
timer.
Bob
On Thu, Jan 19, 2012 at 6:56 AM, Rostam Sohrab <[email protected]>wrote:
>
>
> I have a little confusion in the understanding of RIP timers.
>
> First the basics...
>
> update timer is 30 secs --> Invalid timers should be 3 times of update i.e
> 90secs but the default is 180secs --> Holddown timers should be 3 times of
> update i.e, 90secs but the default is 180secs --> Flush timer, default is
> 240 secs.
>
> Now there are three parts to my question...
>
> The first question might sound silly but for the sake of a clear
> understanding I'll write it.
>
>
> 1. Does the RIP updates timers work is series? i.e after one elapses the
> other starts?
>
> ex: once U-30sec is over --> Invalid starts and runs for 180 secs -->
> Holddown starts and runs for another 180secs --> And finally flush timer
> starts and runs for 240secs.
>
> Here the total time would be 30+180+180+240=630secs until a route is
> flushed out which is looking quite unreasonable!
>
> 2. Does the Invalid, Holddown & flush timers work is parallel?
>
> ex: once U-30sec is over -> Invalid, Holddown runs for 180secs along with
> the flushtimer which runs for 240secs?
>
> Here the total time would be 30+240=270secs until a route is flushed out
> which looks very much acceptable.
>
>
> 3. And why does the Invalid & Holddown timers run in parallel, if all they
> do?
>
> Because at the end of these two timers (IT & HDT) it would take another
> 60secs for flush timer to flush out the route, which means that all the
> timers IT/HDT/FT are kicking off at the same time immediately after update
> timer expires!
>
> I think I'm just complicating what is supposed to be a simple
> understanding!!!
>
> -RS
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_______________________________________________
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www.ipexpert.com
Are you a CCNP or CCIE and looking for a job? Check out
www.PlatinumPlacement.com
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