From: anthony.sequeira@thomson.com
Date: Sat Nov 18 2006 - 04:02:16 ART
I labbed this one up as this post suggests and learned that he was
indeed correct about how the penalty moves....I am so sorry that I do
not have time right now to research the definitive answer <again> - but
I think you should have all the info you need now to ensure that you
will get the dampening behavior required given certain values.
I suggest you lab this up. With "dampen 30 1000 3000 60" the interface
will not dampen in 30 seconds with 3 flaps..
True, the half life is when the value is decayed by half its original
penalty. But since its an exponentially decaying algorithm, the penalty
begins decaying IMMEDIATELY.
What this means is, if you flap the interface with dampening (dampen 30
1000 3000 60) you will see the penalty at 1000 immediately, but then
querying the dampening for the interface again will indicate another
value like 893. And again, 773, etc. until at 30 seconds the value will
be 500 for the first flap.
If you flap it a second time then the penalty will be the original
decayed penalty value at that moment PLUS the new penalty value (e.g.
1000). And the exponential decay begins again. Query the interface and
you will see the penalty between 500 and 1500 and decaying fast. The
same holds true for a third flap.
In short, a suppress value of 3000, as configured, will not dampen the
interface with 3 flaps in 30 seconds because the cumulative penalty will
be < 3000 at the half-life; guaranteed!
________________________________
From: Salman Abbas [mailto:dukelondon@gmail.com]
Sent: Saturday, November 18, 2006 1:40 AM
To: Sequeira, Anthony (NETg)
Cc: hitesh@att.com; ccielab@groupstudy.com
Subject: Re: IP Event Dampening
Hi Hitesh,
Thanks a bunch bro.
Hi Anthony,
Thanks for the thread but what should the answer be, taking Hitesh's
reply and the thread into consideration?
I mean dampening 15 1000 ___ 60 .
Pls advise,
Thanks and Regards,
Salman
On 11/18/06, anthony.sequeira@thomson.com <anthony.sequeira@thomson.com
> wrote:
Careful - this feature does not work like you think - here is an
excellent thread from the archives on the subject. . . note that the
biggest surprise is how the feature uses an exponentially decaying
algorithm - jeez.....
http://adserver.groupstudy.com/archives/ccielab/200605/msg01011.html
Anthony J. Sequeira
#15626
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com ] On Behalf Of
SAVJANI, HITESH, WWCS
Sent: Friday, November 17, 2006 2:54 PM
To: Salman Abbas; ccie >> Cisco certification;
Duane.Fletcher@morganstanley.com
Subject: RE: IP Event Dampening
Salman,
Default value for the penalty is 1000 which can not be changed. Yes, it
increases by 1000 every time it flaps. You are probably looking at the
default suppress value which is 2000 also. However you can configure the
suppress-threshold value which will decide when to suppress a route. You
can read more about it on the following link
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123tcr/1
23tip2r/ip2_c1gt.htm#wp1093971
I am sure someone else on the group can add to this.
HTH,
Hitesh Savjani
CCIE # 17151
________________________________
From: Salman Abbas [mailto: dukelondon@gmail.com]
Sent: Friday, November 17, 2006 1:57 PM
To: SAVJANI, HITESH, WWCS; ccie >> Cisco certification;
Duane.Fletcher@morganstanley.com
Subject: Re: IP Event Dampening
Hi Fletcher,
I'm not the Sal Abbas who used to work at AT&T.
Hi Hitesh,
Thanks a bunch for your reply. The default value for "value to start
suppressing an interface" is 2000. I've checked that on the router.
When you say in 2 flaps, it'll become 2000, do you mean it increases by
1000 every time theres a flap? Is this a documented value somewhere or
can I see this on the router? If it starts from 0, why do I always see a
value of 2000 in my sh dampening interface output?What do you think the
answer should be in the light of this fact?
Regards,
Salman
On 11/18/06, SAVJANI, HITESH, WWCS <hitesh@att.com> wrote:
Salman,
I think if you want your interface to be suppressed after two
flaps then
you should set the value to be 2000.
Reason for that is it will start from 0 penalty & in 2 flaps
will bring
it to 2000.
HTH,
Hitesh Savjani
CCIE # 17151
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf Of
Salman Abbas
Sent: Friday, November 17, 2006 11:36 AM
To: ccie >> Cisco certification
Subject: IP Event Dampening
Hi guys,
I want RIP to stop interface e0/0 on my router from
participating in
routing
if it flaps 2 times in a *15* second period. what dampening
values will
I
have to set to achieve this?
interface e0/0
dampening *15* 1000 __ 60. I think the answer would fit at the
third
place
(value to start supressing an interface) in the dampening
command.
However,
Im not sure. Please help.
Thanks a bunch in advance!!!
Cheers!
Salman
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