Is the export policy selective under valley-free?

William Waites ww at styx.org
Wed Sep 3 05:29:31 CDT 2008


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On 08-09-03 at 11:40, Randy Bush on holiday and should not be
                       reading nanog, let alone responding wrote :

> i assure you that the actual topology is not valley free.  e.g. there
> are many backup or political hack transit paths [0]

Sorry to further impinge on your vacation, but was there a footnote  
there?

> between otherwise peers and there are also backup customer/provider
> reversals.

Perhaps the first case could be called misclassification of the edge by
the link-labelling heuristics (and "otherwise peers" dropped)?

But where such a relationship is symmetric it runs into the second
case, and I agree that the model breaks down in the mutual transit
scenario where a link can look like either c2p or p2c depending on
the path being considered.

How useful/productive is it to say that any observed path is always,
by definition, valley-free and that the labels are not really
properties of the graph but properties of the path? I'm not sure.

Bonne vacances,
- -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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