[131988] in North American Network Operators' Group
Re: AS path question.
daemon@ATHENA.MIT.EDU (Jared Mauch)
Wed Nov 10 15:31:38 2010
From: Jared Mauch <jared@puck.nether.net>
In-Reply-To: <27C3DED6-C314-45CC-970E-2D97CD8E1E38@oicr.on.ca>
Date: Wed, 10 Nov 2010 15:31:25 -0500
To: Greg Whynott <Greg.Whynott@oicr.on.ca>
Cc: "nanog@nanog.org list" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Nov 10, 2010, at 3:22 PM, Greg Whynott wrote:
>=20
>=20
> Recently I adjusted the maxas-limit option on our router, logs =
started reporting routes being refused because the AS path is to long. =
seems to work as expected.
>=20
> when I looked at the logs I was a bit confused at what i was looking =
at... why is it there are multiple AS's in the path that appear to be =
the same AS? I expected an AS path comprised of mostly unique ASs.
>=20
> instead of this:
>=20
> 476330: Nov 10 14:55:07.247 EDT: %BGP-6-ASPATH: Long AS path 549 26677 =
6939 21011 43022 43022 43022 43022 43022 47359 47359 47359 47359 47359 =
47359 47359 47359 received from isp router: More than configured =
MAXAS-LIMIT
>=20
>=20
>=20
> i expected it would look more like:
>=20
> 476330: Nov 10 14:55:07.247 EDT: %BGP-6-ASPATH: Long AS path 549 26677 =
6939 21011 43022 47359 received from =85 .. .
People prepend, and think 'more is better' vs using communities and =
other 'complex' methods of managing their traffic.
It's also the easy tool from the shed. 'set as-path prepend blah' is =
easier than
match blah, set community blah, match something else, set community =
blah2, match something3, set something3
in the typical cisco parlance. It's perhaps better (or worse) depending =
on your vendor and how the policies are actually interpreted and how =
granular you need to be.
The best question is:
Do you know what prefix you just lost reachability to, or do you just =
point default as a last resort anyways, so don't know.
- Jared=
