[195100] in North American Network Operators' Group
Re: Long AS Path
daemon@ATHENA.MIT.EDU (Mel Beckman)
Wed Jun 21 11:49:36 2017
X-Original-To: nanog@nanog.org
From: Mel Beckman <mel@beckman.org>
To: "sthaug@nethelp.no" <sthaug@nethelp.no>
Date: Wed, 21 Jun 2017 15:49:30 +0000
In-Reply-To: <20170621.095626.74671742.sthaug@nethelp.no>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
Steinar,
What reason is there to filter them? They are not a significant fraction of=
BGP paths. They cause no harm. It's just your sense of tidiness.=20
You might consider contacting one of the operators to see if they do have a=
good reason you haven't considered. But absent a good reason *to* filter t=
hem, I would let BGP mechanics work as intended.
-mel beckman
On Jun 21, 2017, at 12:57 AM, "sthaug@nethelp.no" <sthaug@nethelp.no> wrote=
:
>> Just wondering if anyone else saw this yesterday afternoon ?
>>=20
>> Jun 20 16:57:29:E:BGP: From Peer 38.X.X.X received Long AS_PATH=3D3D AS_=
SEQ(2=3D
>> ) 174 12956 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 =
234=3D
>> 56 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 234=
56 =3D
>> 23456 23456 23456 23456 23456 ... attribute length (567) More than confi=
gur=3D
>> ed MAXAS-LIMIT
>=20
> There are quite a few examples of people using stupidly long AS paths.
> For instance
>=20
> 177.23.232.0/24 *[BGP/170] 00:52:40, MED 0, localpref 105
> AS path: 6939 16735 28163 28163 28163 28163 28163 28=
163 28163 28163 28163 28163 28163 28163 28163 28163 28163 28163 262401 2624=
01 262401 262401 262401 262401 262401 262401 262401 262401 262401 262401 26=
2401 262401 262401 262401 262949 52938 52938 52938 52938 52938 52938 52938 =
52938 52938 52938 52938 I
>=20
> I currently have 27 prefixes in my Internet routing table with 40 or
> more ASes in the AS path (show route aspath-regex ".{40,}").
>=20
> I see no valid reason for such long AS paths. Time to update filters
> here. I'm tempted to set the cutoff at 30 - can anybody see a good
> reason to permit longer AS paths?
>=20
> Steinar Haug, Nethelp consulting, sthaug@nethelp.no
