To: Paul Traina <pst@cisco.com> Cc: Havard Eidnes <Havard.Eidnes@runit.sintef.no>, bgpd@merit.edu, routing-wg@ripe.net Subject: Re: More route flaps & inconsistent origins Date: Thu, 13 Oct 1994 18:29:56 -0400 From: "Mark S. Fedor" <fedor@msf.psi.net>
To: bgpd@merit.edu, routing-wg@ripe.net Subject: Re: More route flaps & inconsistent origins Date: Thu, 13 Oct 1994 22:58:15 +0100 From: Havard Eidnes <Havard.Eidnes@runit.sintef.no>
Hi,
again, here is a new route flap report. The villains from the top of the previous report have apparently fixed their problem, but a few ASes again manage to get the dubious position at the top of the list with more than 20.000 route flaps in the 24 hours from Oct 12 03:05 GMT to Oct 13 03:05 GMT.
Again I would like to draw to your attention the fact that some destinations are apparently being originated by more than one AS. These show up in the report with more then one origin. I was under the impression that thsi is an illegal or highly undesireable configuration; I would still like to hear some comments on this issue.
This is not illegal by the BGP RFC, but it is basicly frowned upon by operators and the BGPd community. This usually occurs when people are back-leaking redistributing IGP's into different BGP ASs.
If you were homed to the NSFNET in two different places, you needed unique AS's at each peering point. So you had to dump your nets into two different AS's. I realize this recently changed, but why deal with it now, when it will soon go away.
That hasn't been true for years... anyway, everyone knows that PSI=174:2149 so it's no big deal.
mf
By the way, an interesting statistic here is not so much the originating AS (yes, that is interesting, but...) but rather determining transit ASs that are causing the flaps.
For instance, say AS 109 is transited by AS 200, and AS 200 flaps a lot. AS 109 will show up as flapping and the flaps aren't debited against 200, so you don't discover the real problem.
Paul
* AS's used in this are only for example purposes, no slam against barrnet intended. :-)