From: Jason Madsen (madsen.jason@gmail.com)
Date: Sat Jul 05 2008 - 15:04:37 ART
Li,
Here's a good example from the Doc' CD:
http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp4.html#wp1013542
...just scroll down a little bit 'til you get to the route-map example.
Jason
On Sat, Jul 5, 2008 at 11:36 AM, Jason Madsen <madsen.jason@gmail.com>
wrote:
> Li,
>
> dampening is a bgp mechanism to stop the advertisement of unstable
> routes. each time a router flaps a penalty gets assigned to it. once the
> total penalty value exceeds the suppress limit value, the offending route
> stops getting advertised. then there is a thing called a half life.
> basically it is a time value that reduces the total penalty by a value that
> is initially half of the penalty value. if the route does not flap, the
> total penalty value decreases by half a penalty value amount. each
> successful half life reached causes the half life penalty value to decrease
> by half again and be removed from the total penalty value. this process
> continues and one the total penalty value is less than the reuse limit, the
> route gets advetised again.
>
> so basically here are the controls used by route dampening:
>
> - penalty - numeric value added to a total value each time a route
> flaps.
> - suppress limit - numeric value. when it's exceeded, the offending
> route is no longer advertised.
> - reuse limit - numeric value that establishes the use-again point for
> a route...total penalty value must be less than this value.
> - half life - time to decrease the penalty. when this time increment
> is reached without flapping, the last penalty value halves and then that
> halved value is removed from the total penalty value.
> - max suppress time (didn't explain this control above, but it is used
> to prevent a route from occurring such a large penalty value that it is
> suppressed for a longer than desired time).
>
> here's an example that SHOULD work for your scenario (you only gave us a
> piece of it I think):
>
> penalty - 1000 (default)
> suppress limit - 4000
> reuse limit - 750 (default)
> half-life - 15 minutes (default)
> max suppress time - 60 minutes (default)
>
> are your requirements to suppress the route if it flaps 5 times in a
> minute, or if it flaps more than 5 times in a minute? a suppress limit of
> 4000 works for 5 times in a minute and 5000 works for more than 5 in a
> minute.
>
> i left most of the values at default, because your requirements didn't
> really dictate changing them.
>
> hope this helps,
> Jason
>
> On Sat, Jul 5, 2008 at 8:19 AM, <yungli2008@gmail.com> wrote:
>
>> Hi experts
>> Can anyone guide me to understand how the dampening work in a router?
>> I mean...for example
>> i would like to withdraw a route flap 5 times within one minutes
>> Can anyone help me to understand this?
>> Regards
>> Li
>>
>>
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