Is the export policy selective under valley-free?

Wed Sep 3 15:11:10 UTC 2008

On Wed, Sep 3, 2008 at 4:29 AM, William Waites <ww at styx.org> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Le 08-09-03 à 11:08, Iljitsch van Beijnum a écrit :
>
>> 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, "announce
> 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 are
> 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 the
> valley-free rule contains paths that would not occur in reality.
>
> I think that yes, the valley-free property is a necessary but not sufficient
> criteria for generating the set of in-reality-valid paths on the Internet.
>
> Cheers,
> - -w
> - --
> William Waites                       <ww at styx.org>
> http://www.irl.styx.org/          +49 30 8894 9942
> CD70 0498 8AE4 36EA 1CD7  281C 427A 3F36 2130 E9F5
>
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.9 (Darwin)
>
> iEYEARECAAYFAki+WRAACgkQQno/NiEw6fW/bACeMoPGulTNd0+EiGesbTO8a3cX
> YfEAn2QOy9b3TVbA0t8CANp6BFPfcp8p
> =nYb4
> -----END PGP SIGNATURE-----
>


-- 
-Kai