Alan Hannan said:

Physical topology is likely to map to geographic topology. Circuits certainly do take odd L1 paths to connect L1 endpoints, but these are exceptions, not he rule.

Accordingly, not allocating in a geographic fashion lends to deaggregation, which is bad.

A good sentiment, but not neccessarily practical. The one constant we can count on is that things change.

So, if I look at my crystal ball, and predict that I will need n addresses in a particular physical location, using your planning exemplar I will allocate n addresses in an aggregate. The fact that I only need 1/2 n now means that I will temporarily waste 1/2 n. But what happens when I need n + 1 addresses in that city? Which is the lesser of two evils? So there is also a good argument to *not* rely on a congruence of physical and geographic topology. Some form of NAT still appears preferable.

Rodney Joffe Chief Technology Officer Genuity Inc., a Bechtel company http://www.genuity.net