Is the export policy selective under valley-free?

Valdis.Kletnieks at Valdis.Kletnieks at
Wed Sep 3 12:26:54 CDT 2008

On Wed, 03 Sep 2008 10:36:52 +0200, William Waites said:

> Valley-free is a property of AS mesh models that says that, where edges
> are classified as peering (p2p) or transit (c2p) that a valid path
> contains zero or one peering link and that the peering link occurs
> adjacent to the top of the path. That is that valid paths look like,
> 	[c2p c2p ... c2p p2p p2c ... p2c p2c]

OK, I'm looking at this, and having a *little* trouble buying that there's
exactly zero or one p2p links - consider the case where the last 'c2p' link
is to provider A, who peers with B but not C, and B peers with both A and C,
and the first p2c link lands at C.  Don't you end up with "cp2 p2p p2p p2c" in
that case?  Or is there a convention saying we compress the A-B and B-C
links into a notational A-C link?  Or are we defining A-B or B-C links as
being a c2p type instead, even though they're peering and not transit?

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