From: Jason Madsen (madsen.jason@gmail.com)
Date: Sat Jul 05 2008 - 14:36:20 ART
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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