[195109] in North American Network Operators' Group
Re: Long AS Path
daemon@ATHENA.MIT.EDU (Pierfrancesco Caci)
Thu Jun 22 02:09:49 2017
X-Original-To: nanog@nanog.org
From: Pierfrancesco Caci <pf@tippete.net>
To: "nanog\@nanog.org" <nanog@nanog.org>
Date: Thu, 22 Jun 2017 08:09:41 +0200
In-Reply-To: <4FF09308-6FF0-4B72-9AEE-2A5C33852800@beckman.org> (Mel Beckman's
message of "Wed, 21 Jun 2017 20:45:16 +0000")
Reply-To: Pierfrancesco Caci <pf@tippete.net>
Errors-To: nanog-bounces@nanog.org
>>>>> "Mel" == Mel Beckman <mel@beckman.org> writes:
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. Blindly
Mel> limiting otherwise legal path lengths is not a defensible practice, in
Mel> my opinion.
Mel> -mel beckman
A prepend like that is usually the result of someone using the IOS
syntax on a XR or Junos router.
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.
As a data point, here is how many prefixes I see on my network for each
as-path length, after removing prepends:
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
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.
Pf
--
Pierfrancesco Caci, ik5pvx
