[isp-bgp] Re: BGP routing loop !

[Erblichs <erblichs@...>]

Willia, et al,

	I remember a vendor specific support for
	two or more of the same AS within the path.

	The reasoning behind was that the AS was
	traversed twice because the AS was either
	partitioned and/or a external path was
	determined to better than traversing a
	particular path within the AS.

	In cases other than the above, IMO,yes the same
	AS can be an indication of a routing loop.

	Mitchell Erblich
	Consulting Sr Software Engineer
	---------------------

"william(at)elan.net" wrote:
> 
> On Sat, 7 Aug 2004, Gojko Vujovic wrote:
> 
> > Kave Salamatian wrote:
> > > Hello Folks,
> > >
> > > I have a practical BGP question. I am receiving the following AS paths:=20
> > > 2200 5511 702 8342 29651 25515 29369 25515=20
> > >
> > > With the AS 25515 repeated two times with the AS 29369 in the middle.  = Is
> > > it normal?
> >
> > Yes, it is normal. It's called route prepending and has nothing to do
> > with routing loops. It is mostly used to choose a preferred route for
> > some traffic.
> 
> But its a real problem when you're trying to analyze bgp data or put it
> into structured database. There it would be loop which does not fit into
> otherwise all-forward bgp tree system. And this is unlike normal
> prepending where it its all the same ASN (i.e. like 29651 25515 25515 25515)
> and which do not break all-forward bgp path.
> 
> --
> William Leibzon
> Elan Networks
> william@...
> 




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