[83867] in North American Network Operators' Group
Re: Order of ASes in the BGP Path
daemon@ATHENA.MIT.EDU (Abhishek Verma)
Mon Aug 29 20:49:04 2005
Date: Tue, 30 Aug 2005 06:18:30 +0530
From: Abhishek Verma <abhishekv.verma@gmail.com>
To: Richard A Steenbergen <ras@e-gerbil.net>
Cc: nanog@nanog.org
In-Reply-To: <20050829170213.GB8847@overlord.e-gerbil.net>
Errors-To: owner-nanog@merit.edu
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I thank everyone who took time off their busy schedules and answered me on=
=20
this. I now understand that people do look at the AS_PATH and the order of=
=20
ASes is important for debugging, etc.
Regards,
Abhishek
On 8/29/05, Richard A Steenbergen <ras@e-gerbil.net> wrote:=20
>=20
> 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?
>=20
> 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 unordere=
d
> 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.
>=20
> 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. :)
>=20
> --
> Richard A Steenbergen <ras@e-gerbil.net> http://www.e-gerbil.net/ras
> GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC=
)
>=20
--=20
--
Computer Science Deptt.
Institute of Technology, BHU
Varanasi - India
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<div>I thank everyone who took time off their busy schedules and answered m=
e on this. I now understand that people do look at the AS_PATH and the orde=
r of ASes is important for debugging, etc.</div>
<div> </div>
<div>Regards,</div>
<div>Abhishek<br><br> </div>
<div><span class=3D"gmail_quote">On 8/29/05, <b class=3D"gmail_sendername">=
Richard A Steenbergen</b> <<a href=3D"mailto:ras@e-gerbil.net">ras@e-ger=
bil.net</a>> wrote:</span>
<blockquote class=3D"gmail_quote" style=3D"PADDING-LEFT: 1ex; MARGIN: 0px 0=
px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">On Mon, Aug 29, 2005 at 10:15:26=
PM +0530, Abhishek Verma wrote:<br>><br>> Hi,<br>><br>> Is the =
order of AS numbers (except for perhaps the first one which
<br>> denotes the AS the route was originated from) in the AS_PATH in BG=
P<br>> important? In fact, does anybody even care for the first AS numbe=
r<br>> that appears in the Path?<br>><br>> AFAIK, AS numbers in th=
e BGP serves two purposes. It helps in loop
<br>> detection and it helps us count the AS Path length.<br>><br>>=
; If this is the case then the order should not really matter much.<br>>=
<br>> My question is that whether the operators care if the order, for s=
ome
<br>> reason changes?<br><br>Just that pesky little thing called sanity,=
aka having a hope in hell of<br>being able to figure out which network is =
connected to which and in what<br>order. While it is technially possible to=
run everything with an unordered
<br>AS-PATH set, it is so rare that "most" people looking at AS-P=
ATHs either<br>don't know it is possible, or don't take its possibility int=
o account<br>properly.<br><br>Besides being likely to confuse the hell out =
of a lot of people, you're
<br>even more likely to break someone's BGP querying perl scripts. I wouldn=
't<br>underestimate the amount of that stuff out there either, especially i=
n<br>areas like abuse tracking/reporting. Basically you'd be making a gener=
al
<br>pain in the ass out of yourself, so hopefully you have a damn good reas=
on<br>for it. :)<br><br>--<br>Richard A Steenbergen <<a href=3D"mailto:r=
as@e-gerbil.net">ras@e-gerbil.net</a>> &nbs=
p; <a href=3D"http://www.e-gerbil.net/ras">
http://www.e-gerbil.net/ras</a><br>GPG Key ID: 0xF8B12CBC (7535 7F59 8204 E=
D1F CC1C 53AF 4C41 5ECA F8B1 2CBC)<br></blockquote></div><br><br clear=3D"a=
ll"><br>-- <br>--<br>Computer Science Deptt.<br>Institute of Technology, BH=
U
<br>Varanasi - India<br>
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