[107388] in North American Network Operators' Group
Re: Is the export policy selective under valley-free?
daemon@ATHENA.MIT.EDU (William Waites)
Wed Sep 3 05:30:11 2008
From: William Waites <ww@styx.org>
To: Iljitsch van Beijnum <iljitsch@muada.com>
In-Reply-To: <4EF4ADA5-960A-4B5E-8D56-A364E543046F@muada.com>
Date: Wed, 3 Sep 2008 11:29:52 +0200
Cc: nanog@merit.edu
Errors-To: nanog-bounces@nanog.org
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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 =20
>> 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, =20
"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] =20
that are
not allowed because of A's policy. Though such a policy might be =20
unusual,
this is a case where the set of paths generated from the topology with =20=
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 =20
sufficient
criteria for generating the set of in-reality-valid paths on the =20
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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