Order of ASes in the BGP Path

Tue Aug 30 00:48:30 UTC 2005

I thank everyone who took time off their busy schedules and answered me on 
this. I now understand that people do look at the AS_PATH and the order of 
ASes is important for debugging, etc.
 Regards,
Abhishek

 On 8/29/05, Richard A Steenbergen <ras at e-gerbil.net> wrote: 
> 
> On Mon, Aug 29, 2005 at 10:15:26PM +0530, Abhishek Verma wrote:
> >
> > Hi,
> >
> > Is the order of AS numbers (except for perhaps the first one which
> > denotes the AS the route was originated from) in the AS_PATH in BGP
> > important? In fact, does anybody even care for the first AS number
> > that appears in the Path?
> >
> > AFAIK, AS numbers in the BGP serves two purposes. It helps in loop
> > detection and it helps us count the AS Path length.
> >
> > If this is the case then the order should not really matter much.
> >
> > My question is that whether the operators care if the order, for some
> > reason changes?
> 
> Just that pesky little thing called sanity, aka having a hope in hell of
> being able to figure out which network is connected to which and in what
> order. While it is technially possible to run everything with an unordered
> AS-PATH set, it is so rare that "most" people looking at AS-PATHs either
> don't know it is possible, or don't take its possibility into account
> properly.
> 
> Besides being likely to confuse the hell out of a lot of people, you're
> even more likely to break someone's BGP querying perl scripts. I wouldn't
> underestimate the amount of that stuff out there either, especially in
> areas like abuse tracking/reporting. Basically you'd be making a general
> pain in the ass out of yourself, so hopefully you have a damn good reason
> for it. :)
> 
> --
> Richard A Steenbergen <ras at e-gerbil.net> http://www.e-gerbil.net/ras
> GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)
> 

-- 
--
Computer Science Deptt.
Institute of Technology, BHU
Varanasi - India
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