On Wed, Sep 3, 2008 at 4:29 AM, William Waites <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> > 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
