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 <j...@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 > -- [stillwa...@gmail.com ~]$ cat .signature cat: .signature: No such file or directory [stillwa...@gmail.com ~]$
