[195115] in North American Network Operators' Group
Re: Long AS Path
daemon@ATHENA.MIT.EDU (Mel Beckman)
Thu Jun 22 10:25:47 2017
X-Original-To: nanog@nanog.org
From: Mel Beckman <mel@beckman.org>
To: jim deleskie <deleskie@gmail.com>
Date: Thu, 22 Jun 2017 14:25:40 +0000
In-Reply-To: <CAJL_ZMNz2LCEzH2tQHdivVUUmTkU6rOKgm9DK=x9aoojtrj0vA@mail.gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
You don't have to wonder. You can call and ask them.=20
-mel via cell
> On Jun 22, 2017, at 5:47 AM, jim deleskie <deleskie@gmail.com> wrote:
>=20
> I see 5+ prepends as maybe not reason to have your "BGP driving license
> revoked" but if I can continue with the concept that you have your BGP
> learners permit.
> If I think back to when I learned to code or when making ACL's, we still
> used line number and practice would be to give ourselves lots
> of space 5 or 10 numbers in case we have to insert something in the middl=
e.
> ie I need 2 sets of prepends, I'm still learning this stuff
> so I'll go with 5 and 10. We all started somewhere, we all did dumb stuff=
,
> hopefully, we all learned.
>=20
> 12AS hops, I have to go see how they are connected now, maybe someone in
> that chain needs to be invited by an IX to a NANOG or GPF or some such,
> that can't be super efficient.
>=20
> -jim
>=20
> On Thu, Jun 22, 2017 at 3:09 AM, Pierfrancesco Caci <pf@tippete.net> wrot=
e:
>=20
>>>>>>> "Mel" =3D=3D Mel Beckman <mel@beckman.org> writes:
>>=20
>>=20
>> Mel> Why not ask the operator why they are pretending this path?
>> Perhaps
>> Mel> they have a good explanation that you haven't thought of. Blindl=
y
>> Mel> limiting otherwise legal path lengths is not a defensible
>> practice, in
>> Mel> my opinion.
>>=20
>> Mel> -mel beckman
>>=20
>>=20
>> A prepend like that is usually the result of someone using the IOS
>> syntax on a XR or Junos router.
>>=20
>> Long ago, someone accidentally prepending 255 times hit a bug (or was it
>> a too strict bgp implementation? I don't remember) resulting in several
>> networks across the globe dropping neighbors. One has to protect against
>> these things somehow.
>>=20
>> As a data point, here is how many prefixes I see on my network for each
>> as-path length, after removing prepends:
>>=20
>>=20
>> aspath length count
>> -------------------------
>> 0: 340
>> 1: 47522
>> 2: 292879
>> 3: 227822
>> 4: 58390
>> 5: 10217
>> 6: 2123
>> 7: 638
>> 8: 48
>> 9: 58
>> 11: 20
>> 12: 2
>>=20
>>=20
>> So, does your customer have a legitimate reason to prepend more than 5
>> times? Maybe. I still think that anyone that does should have their BGP
>> driving licence revoked, though.
>>=20
>> Pf
>>=20
>>=20
>>=20
>>=20
>> --
>> Pierfrancesco Caci, ik5pvx
>>=20
