nanog mailing list archives

Re: Dampening considered harmful?


From: Mark Kent <mark () noc mainstreet net>
Date: Mon, 27 Dec 2004 18:16:24 -0800 (PST)


Back in mid-December someone typed:

One reason to be careful with dampening is that flaps can be 
multiplied. (Connect to routeviews and see the different flap counts 
under different peers for the same flap at your end to observe this.)

How about in this scenario:

  asA gets transit from asT
  asA gets backup transit (ASpath padding) from asB
    asB gets transit from asT
    asB gets transit from asJ
      asJ gets transit from asT
        asT peers with whole world(*)

Now, as asA flaps to asT, we see "bad things" happen to their routes,
namely an unreasonable amount of flap at even nearest neighbors to asT.

Can this flap magnification be explained by the hierarchy I describe
above?  That is, asT treats all of these ASpaths as customer routes:

  asA
  asB_asA
  asJ_asB_asA

and so we might expect to see multiple flaps as different "best"
routes come into view inside the geographically diverse asT...  right?

Thanks,
-mark

(*)you know what I mean.


Current thread: