NAT is a dead end. If the Internet does not develop a way to obsolete
NAT, the Internet will die. It will gradually be replaced by networks
that are more-or-less IP based but which only run a small number of
applications, poorly, and expensively.
...or you will see an overlay network build on top of NAT+IPv4 that
abstracts the shortcomings away - aka what the peer to peer networks are
doing. End-to-end addressing...
the overlay networks depend on having some hosts that aren't behind a
NAT to serve as tunnel endpoints for hosts that do. this will become
less viable in the future as IPv4 address space gets more and more scarce.
also, for the most part, overlay networks do not perform as well as
native networks (there are exceptions, as in bittorrent). so they do
not abstract (all of) the shortcomings away.
OTOH, one transition path away from NATs might be to extend NATs so that
they support creation of overlay networks. such devices could also aid
v4/v6 coexistence.
Keith
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