Is the export policy selective under valley-free?

William Waites ww at styx.org
Wed Sep 3 04:29:52 CDT 2008


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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"

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

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