rfd

Michael Still stillwaxin at gmail.com
Wed Dec 19 05:29:52 UTC 2018


In general I agree with the idea here but I would also be interested in the
possibility of running the local route policy engine against routes that
are locally detected to meet a damping condition (user configureable of
course). This would potentially yield the ability to change local_pref as
well as other attributes that may be useful such as MED/metric (which can
be transitive) and/or communities.

On Tue, Dec 18, 2018 at 4:55 PM Job Snijders <job at ntt.net> wrote:

> Dear Steve,
>
> No worries, I have not forgotten the transitive properties of the
> LOCAL_PREF BGP Path Attribute! :-) You are right that any LOCAL_PREF
> modifications (and the attribute itself), are local to the Autonomous
> System in which they were set, but the effects of such settings can
> percolate further into the routing system.
>
> A great example is the "BGP Graceful Shutdown" mechanism (science
> partially documented in https://tools.ietf.org/html/rfc6198, actual
> specification here https://tools.ietf.org/html/rfc8326). What is
> interesting is that by considering a path (any path, could be flapping)
> my network will propagate alternative paths to my neighboring networks,
> or possibly even *withdraw* my announcement in favor of alternative
> (stable?) paths via competitors.
>
> By attaching a lower LOCAL_PREF value to a given path for a period of
> time as a 'penalty' for flapping, I suspect the visiblity of that
> flapping will be greatly reduced. This of course doesn't hold true when
> the only origin of the path is flapping, but in many flapping cases I
> triaged it was clear that only one out of many links was the root of the
> flapping.
>
> I'm not sure I share your concerns about scale, it appears that so far
> we seem to be doing just fine without "route flap dampening, penalty
> type: suppress". No customers ask for it, in fact many are relieved we
> don't use it. None of our peering partners ask for it either. When we
> see oscillating paths we reach out to the offending party and ask them
> to fix it, or take unilateral action within a specific time frame.
>
> Kind regards,
>
> Job
>


-- 
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