On Wed, Sep 3, 2008 at 4:29 AM, William Waites <ww@styx.org> wrote:
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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@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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-- -Kai