[isp-bgp] Re: BGP routing loop !

[Charles Gucker <cgucker@...>]

On Wed, 4 Aug 2004 11:28:48 +0200, Kave Salamatian <salamat@rp.lip6.fr> 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?
> 
> Can a BGP guru answer me.

Hrm, sure I'll bite.  The BGP path you show could be generated in a
number of ways.  If you have a traceroute to accompany it, it would
certainly help.   But from my vantage point this could happen in one
of a couple ways.  The most obvious is that AS 25515 is inproperly
prepending their AS in the AS_PATH.
The only way to figure this out would be look at this route from their
upstream's vantage point (which is what the traceroute would help
figure out).  The second would be that AS 29369 is inproperly setting
their
prepends towards AS29651 (their upstream).

The other train of thought is that somebody has some poor filters
setup leaking this route when they shouldn't be.  Bad bad non-dynamic
originating filter evil-doers! ;-)

thanks,
charles







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