Keith,
One more observation at the intersection between my earlier note
to you and the one to Tony...
In the presence of an adequate abstraction model, an application
should not care whether a given host has one address or a dozen,
nor about whether such addresses were equivalent or different,
nor about whether they represent physically separate interfaces.
Indeed, one might suggest that the level of opacity that lack of
application-visible differentiation implies would be a useful
test for an adequate abstraction.
john