From: Yung Li (yungli2008@gmail.com)
Date: Sat Jul 05 2008 - 16:03:55 ART
Thanks Mr.Jason Madsen
On 7/5/08, Jason Madsen <madsen.jason@gmail.com> wrote:
>
> 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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