route flap dampening

Mon Apr 27 19:13:09 UTC 2009

We're using Cisco 6509 MSFC2s for core engines with three 85% route
feeds and Cisco-default route flap suppression. Yeah, the default flap
suppression parameters are aggressive but we want to be sure we don't
hog precious CPU cycles from a nasty route flap and provide more
consistent routes to our downstreams. We can't take a full route table
(232k) due to TCAM limitations, so we have default routes anyway.
There's only a subtle impact to our customers with maybe a less
preferable, stable path versus a better, flapping one. A better
bargain in our book, but maybe not for others... CPU runs around
10-12% all day.

If we had more router CPU and no default routes, we'd probably have
dampening enabled but at very high thresholds under similar network
policies.

-D

On Mon, Apr 27, 2009 at 2:35 PM, Jack Bates <jbates at brightok.net> wrote:
> Patrick W. Gilmore wrote:
>>
>> On Apr 27, 2009, at 2:20 PM, Jack Bates wrote:
>>>
>>> We've been considering it after the last flap around the world; perhaps
>>> with extremely short penalty times.
>>
>>
>> <http://www.ripe.net/ripe/meetings/ripe-43/presentations/ripe43-routing-flap.pdf>
>>
>
> Yeah, read the presentation several times, thus the short penalty times, and
> probably high thresholds.
>
> The idea for me is to limit the harm of excessive flapping while not being
> paranoid. I've had a customer lose a lot of connectivity for 30 minutes
> after 3 or 4 flaps. I figure 5 minute ignore after about 10 flaps in a  10
> minute period.
>
> Jack
>
>