[107386] in North American Network Operators' Group
Re: Is the export policy selective under valley-free?
daemon@ATHENA.MIT.EDU (William Waites)
Wed Sep 3 04:37:05 2008
From: William Waites <ww@styx.org>
To: Paul Wall <pauldotwall@gmail.com>
In-Reply-To: <620fd17c0809021723w36693b2ctd3731a4bf706f5d9@mail.gmail.com>
Date: Wed, 3 Sep 2008 10:36:52 +0200
Cc: NANOG list <nanog@merit.edu>
Errors-To: nanog-bounces@nanog.org
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Le 08-09-03 =E0 02:23, Paul Wall a =E9crit :
>
> That's correct. A network purchasing transit will advertise its
> internally-originated prefixes, as well as those it's learning from
> downstream customers, to its provider.
>
> I'm not sure what "valley-free" means in this context. You might want
> to try the Rosetta Stone patches and make sure your copy is up to
> date.
Valley-free is a property of AS mesh models that says that, where edges
are classified as peering (p2p) or transit (c2p) that a valid path
contains zero or one peering link and that the peering link occurs
adjacent to the top of the path. That is that valid paths look like,
[c2p c2p ... c2p p2p p2c ... p2c p2c]
(slightly abusing the notation for clarity)
The idea is that a small, customer AS should not provide transit between
its upstreams, though this does, apparently happen sometimes.
Barring misconfigurations, I believe that AS paths are normally valley-
free.
See, for example,
"Toward Valley-Free Inter-domain Routing"
http://nsrc.cse.psu.edu/tech_report/NAS-TR-0054-2006.pdf
"AS Relationships: Inference and Validation"
=
http://www.caida.org/publications/papers/2006/as_relationships_inference/
Cheers,
- -w
- --
William Waites <ww@styx.org>
http://www.irl.styx.org/ +49 30 8894 9942
CD70 0498 8AE4 36EA 1CD7 281C 427A 3F36 2130 E9F5
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