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Re: Flapping /16 prefix, why?

  • From: Skutch
  • Date: Mon Feb 24 20:44:02 1997

Sprint does indeed dampen customer paths, and often.


On Fri, 21 Feb 1997, Jim Rowh wrote:

> The degree of prepending you show is probably more for Sprint's 
> benefit than anyone else's. 1793, 1239, and 1790 are all Sprint AS's. 
> If you're lucky, you can find someone familiar with Sprint's 
> confederated routing scheme to explain the details. AS3505 
> belongs to VNet, who uses both Sprint and Gridnet as providers. Prepending 
> allows them (VNet) to effectively designate Gridnet as their primary 
> (all things being equal, better--shorter--AS path wins).
> 
> As for hold-down routes (to Null0) and damping, yes, they're both 
> good and generally practiced ideas. As to whether and to what extent 
> Sprint uses either or both of them, you will have to take that up 
> with them: [email protected] or 1-800-230-5108
> 
> 
>  jim
> 
> 
> 
> > Sorry for littering NANOG with this email, but I'm hoping for a little
> > education on this matter from some of the larger National Service
> > Providers.
> > 
> > This morning we had a customer call in concerning a network hole.
> > Upon investigation, I found the following..
> > 
> > BGP routing table entry for 166.82.0.0/16, version 541808
> > Paths: (1 available, best #1, advertised over IBGP, EBGP)
> >   1793 1239 1790 3505 3505
> >     144.228.159.17 from 144.228.159.17 (144.228.159.1)
> >       Origin IGP, metric 0, valid, external, best
> >       Community: 1
> >       Dampinfo: penalty 656, flapped 18 times in 02:19:29
> > 
> > Two immediate things came to mind here.  
> > 
> > 1.	This is a /16 that is flapping.
> > 2.	The end user is using AS path prepending for some reason.
> > 
> > With these two facts in mind, the following questions arise.
> > 
> > Anchoring or tying down of a route with a static route to null seems
> > to be a very basic idea (far more basic that AS path prepending), so 
> > why isn't this route tied down?
> > 
> > I only see one route to this prefix, why are they prepending?  (I admit
> > that only the user of this prefix can answer this question, and I also 
> > admit that with 53 flaps on the books so far, the other provider may
> > be dampening the route for us *thank you*)
> > 
> > Finally, does Sprint not apply *any* dampening to customer routes?
> > 
> > 
> > 
> > My cat is long dead (10 years at least), so it's safe from my curiosity.
> > 
> > Chris A. Icide
> > Nap.Net, L.L.C.
> > 
> > 
> 
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