Customer AS

What would happen if the customer used private address space and NAT
& ALGs to hook this into the two providers' CIDR space? At worst,
address space consumption would be doubled (if the customer really
needs a full /24 internally),

And at best it's quite likely to be reduced. PIXen et al. work
fine on internal networks of 1000s of machines with only one
external class C acting as pool address space. And of course
the cost of the PIX is probably comparible to the cost of the
(larger) router often needed to carry full routing.

Alex Bligh
Xara Networks