From: Thomwin Chen (thomwin_chen@yahoo.com)
Date: Sat Oct 29 2005 - 09:29:06 GMT-3
Hi Dave,
the most minimum penalty value that interface can have is 2000.
and it happens if it flaps 2 times in the very first time, and 1 more time in the very last time (seconds 30th).
2 times flap in the very first time the penalty is 2000, and at the seconds 30th, the penalty value is decreased to 1000.
because 1 more flap in the second 30th, the penalty value is 2000. and this is the minimum.
you can try any 3 flaps combination during 30 seconds interval, and you will find that the minimum penalty value will be get if it flaps 2 times in the very first time (seconds 0), and one more time in the very last time (seconds 30th).
the most maximum penalty value that interface can have during this 30 seconds is 3000.
and it happens if it flaps 3 times in the very first time.
so, to guarantee it will be suppressed if it flaps 3 times in 30 seconds we must set it to :
dampening 30 1000 2000 120
hopefully you follow my sentences,
as I am not good in English.
Rgds,
Thomwin.
Dave Temkin <dave@ordinaryworld.com> wrote:
OK, so let's say it's 3 flaps in 30 seconds... How does the calculation
work then? 30/3000?
On Mon, 24 Oct 2005, simon hart wrote:
> Hi Milenko,
>
> You bring up some fascinating points with regards to this suppression
> question. However I believe the question related to interface dampening as
> opposed to BGP dampening, thus the times are expressed in seconds rather
> than minutes, thus the rate at which the penalty decreases is far more rapid
> (however the overall philosophy still holds).
>
> So if we take the worst case scenario, do we use a suppress of 3000 ?? If
> so the interface would be dampened after 4 flaps and not 5. Anything used
> as a suppress-threshold of less than 4000 will mean the interface could get
> dampened after 4 flaps!!!, But also means that the interface could
> potentially not get dampened after 30 seconds.
>
> And you are right regarding the reuse threshold, in the example I gave there
> is potential for the route to get unsurpressed within that 30 second period.
> However the question does not state how long it should be surpressed for, so
> becoming unsurpressed within 30 seconds should not be an issue.
>
> My conclusion is that it is impossible to answer this question with values
> that will meet every criteria for flapping. If I had this question in the
> lab, I think I would argue the point with the proctor.
>
> I think the question would only make sense if it was geared to 2 flaps in 30
> seconds or 3 flaps in 30 seconds.
>
> More thoughts ?????
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Milenko Markov
> Sent: 24 October 2005 21:44
> To: 'simon hart'
> Cc: ccielab@groupstudy.com
> Subject: RE: Route Dampening
>
>
> Simon,
>
> lets observe "worst case scenario" (?) : 4 flaps "in" first second, and 1
> flap in last (30').
>
> Penalty would be (4x1000/2)+1000=3000...route would not be suppressed ?
>
> I *think* that here two more values playes their role (marked with *) :
>
> 1. "Half-life-Once the route has been assigned a penalty, the penalty is
> decreased by half after the half-life period (which is 15 minutes by
> default). The process of reducing the penalty happens every *5 seconds*."
>
> and
>
> 2. " Reuse limit-As the penalty for a flapping route decreases and falls
> below this reuse limit, the route is unsuppressed. That is, the route is
> added back to the BGP table and once again used for forwarding. The default
> reuse limit is 750. The process of unsuppressing routes occurs at
> *10-second* increments. Every 10 seconds, the router finds out which routes
> are now unsuppressed and advertises them to the world."
>
>
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr
> _c/ipcprt2/1cfbgp.htm#wp1002395
>
>
> more ideas ?
>
> regards,
> Milenko.
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> simon hart
> Sent: 24. oktobar 2005 22:31
> To: Charles Cahoon; ccielab@groupstudy.com
> Subject: RE: Route Dampening
>
> Charles,
>
> You will get a penalty of 1000 for each flap. Your half-life will default
> to 30 seconds (best to leave it there).
>
> You need to work out what to suppress at
>
> If you flapped immediately 5 times in the first couple of seconds you will
> get a penalty of 5000, however a figure of 5000 does not work in the
> following scenario:-
>
> If you flapped 2 times in the first second = 2000 and then flapped 3 times
> in the last couple of seconds you will get a penalty of
>
> roughly 2000/2 = 1000 + 3000 Therefore you will need a suppress-threshold
> of 4000 or above, but below 5000
>
> I would probably go for 4001 - any comments on this figure appreciated.
>
> So
> Half-life = 30
> Suppress-threshold = 4001
> Reuse-threshold = Arbitary for this exercise, however I would go with Cisco
> recommendation of suppress-threshold = reuse*2, therefore 2000
> Max-suppress = leave at default (60)
>
> Simon
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Charles Cahoon
> Sent: 24 October 2005 20:30
> To: ccielab@groupstudy.com
> Subject: Route Dampening
>
>
> Looking for a simple explanation,
>
> I have read a great deal about how to dampen but it's not getting any
> clearer
> for me. I was hoping that someone can help.
>
> My question is if I want to remove a route if it flaps 5 times in 30
> seconds?
>
> Using the "Half-Life, Suppress Threshold, Reuse Threshold and Maximum
> Suppress
> time" not sure these correlate, what am I missing?
>
> Thanks for the help
>
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