From: ccie2be (ccie2be@nyc.rr.com)
Date: Sun Jul 17 2005 - 10:41:19 GMT-3
Swaroop,
You must have missed the post from Marvin Greenlee on this.
<Quote>
Dampening for an interface uses a half life value in seconds. With a range
of 1-30 seconds, the penalty will decay very quickly.
IP Event Dampening
http://www.cisco.com/en/US/products/sw/iosswrel/ps1838/products_feature_guid
e09186a0080134a41.html#wp1048359
With that in mind, your half life value can be a maximum of 30 seconds.
So, let's say your interface flaps once a minute for the first 6 minutes and
consider the penalty of the first flap over that period.
Also assume that the first flap takes place immediately at T=0.
So, at T=0, the penalty = 1000.
At T=30 in seconds, the penalty = 500
AT T=60, the penalty = 250 plus the penalty for the 2nd flap or 1250.
At T=90, the total penalty = 625.
At T=120, the penalty = 312.5 plus the penalty for the 3rd flap or 1312.5
At T=150, the penalty = 656.25
At T=180, the penalty = 328.125 plus the penalty for the 4th flap or 1328.12
At T=210, the penalty = 664
At T=240, the penalty = 332 plus the penalty for the 5th flap or 1332.
So, after 4 minutes and 5 flaps, the penalty is only 1332.
You still have a long time to go and many more flaps are needed before you
reach the suppress threshold of 6000.
Now, look at the total penalty amount at the end of each minute. It starts
out at 1000. And, you end up with this series:
1000, 1250, 1312, 1328, 1332, etc
Notice how after each minute the difference between the current penalty and
the previous penalty keeps getting smaller and smaller.
With a maximum half life of 30 seconds and a flap rate of once per minute,
as you can see, it will take a very long time to reach your suppress
threshold of 6000.
Since the half life is already set to it's max, the only other variable you
change is the suppress threshold which would need to be much, much lower.
Given the unlikelihood that cisco would tell you exactly when and how often
the interface would flap and the time consuming nature of the calculations,
I highly doubt you would get a task worded that way.
So, my advice is to understand how this works and move on to other topics.
HTH, Tim
-----Original Message-----
From: Swaroop Potdar [mailto:swarooppotdar@hotmail.com]
Sent: Sunday, July 17, 2005 8:03 AM
To: ccie2be@nyc.rr.com; buesink@fma.nl; ccielab@groupstudy.com
Subject: RE: Interface Dampening
Hi,
how would be
max-supress of 3600
supress threshold of 6000
reuse threshold of 499
half-time of 900
would this serve the purpose if the interface has to be kept dampned if it
flaps 6 times in an hour.
????
>From: "ccie2be" <ccie2be@nyc.rr.com>
>Reply-To: "ccie2be" <ccie2be@nyc.rr.com>
>To: <buesink@fma.nl>, <ccielab@groupstudy.com>
>Subject: RE: Interface Dampening
>Date: Thu, 14 Jul 2005 17:35:40 -0400
>
>Hi,
>
>I'll take a crack at this.
>
>Every time the interface flaps, it incurs a penalty of 1000 points (this
>penalty amount is not configurable).
>
>However, you can specify the suppress amount which in your case is at least
>6 x 1000 or 6000 points. (This suppress amount actually has to be lower
>than
>6000 because the penalty starts to decay immediately.)
>
>But, you're not done yet. Once a penalty occurs, it starts to decay at a
>rate of 1/2 the penalty amount per half life. In other words, if the half
>life is 30 minutes, 30 minutes after the penalty occurs, the penalty is
>only
>500 points.
>
>So, now the problem is to figure out how to get to a penalty of 6000 with 6
>flaps in an hour. If there weren't this penalty decaying aspect, this
>would
>be easy. But, with this decaying aspect, the answer depends on when within
>the first hour the flaps occur.
>
>If all 6 flaps occur in the last minute of the hour than there won't be
>much
>time for the penalty to decay much so if your suppress level is should be
>something like this:
>
>total penalties - decay amount > suppress level
>
>So, in your case, total penalties is 6000. Decay amount depends on half
>life where the greater the half-life, the smaller the decay amount. So, if
>you set the suppress level to 5001 and set a very large half you should be
>OK.
>
>HTH, Tim
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>buesink@fma.nl
>Sent: Thursday, July 14, 2005 4:49 PM
>To: ccielab@groupstudy.com
>Subject: Interface Dampening
>
>Hi there,
>
>I've a question, I'm playing with interface dampening.
>And I am always messing things up with it ;-)
>
>I want to do the following:
>
>If an interface flaps 6 times within an hour, then I want to dampen it.
>
>How can I set this up?
>
>
>Regards!
>
>_______________________________________________________________________
>Subscription information may be found at:
>http://www.groupstudy.com/list/CCIELab.html
>
>_______________________________________________________________________
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Regards,
Swaroop.
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