[107398] in North American Network Operators' Group
Re: Is the export policy selective under valley-free?
daemon@ATHENA.MIT.EDU (Kai Chen)
Wed Sep 3 11:11:16 2008
Date: Wed, 3 Sep 2008 10:11:10 -0500
From: "Kai Chen" <kch670@eecs.northwestern.edu>
To: "William Waites" <ww@styx.org>
In-Reply-To: <118AB17C-DEA7-49AA-9E1C-E51798DAE326@styx.org>
Cc: nanog@merit.edu
Errors-To: nanog-bounces@nanog.org
On Wed, Sep 3, 2008 at 4:29 AM, William Waites <ww@styx.org> wrote:
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> Le 08-09-03 =E0 11:08, Iljitsch van Beijnum a =E9crit :
>
>> On 3 sep 2008, at 1:45, Kai Chen wrote:
>>
>>> Just want to ask a direct question. Will an AS export all it gets from
>>> its customers and itself to its providers? Or even under valley-free,
>>> the BGP export policy is also selective?
>>
>> I get the valley-free but not the selective. :-)
>
>
> (guessing)
>
> Suppose,
>
> C1 P1
> \ /
> A
> / \
> C2 P2
>
> Suppose A has different policies for its two customers, such as, "announc=
e
> C1 routes to P1 but not P2" and "announce C2 routes to P2 but not P1"
>
This is exactly what I think? But I am not sure if it is ture. My
observation is that Routeviews cannot see a lot p2c(c2p) links which
they should see if it is strict "valley-free" --- an AS will export
all its customers to every neighbor.
> In this case there would be valley-free paths [C1 A P2], [C2 A P1] that a=
re
> not allowed because of A's policy. Though such a policy might be unusual,
> this is a case where the set of paths generated from the topology with th=
e
> valley-free rule contains paths that would not occur in reality.
>
> I think that yes, the valley-free property is a necessary but not suffici=
ent
> criteria for generating the set of in-reality-valid paths on the Internet=
.
>
> 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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--=20
-Kai
