From: Christian Huitema [huitema(_at_)microsoft(_dot_)com]
Of course, NAT does not really solve multi-homing either -- it is one
of the points where the brittleness is most apparent. But NAT's do
hide the internals of a network, and do isolate networks from
renumbering issues. NAT also break lots of applications, which is why
so many of us hate them. But so do firewalls, and it seems that IPv6
firewalls are encouraged. Oh well.
To a great extent, NATs allow the organization network to be managed
without great concern for anything which happens in the external
network. And in any organization, what happens inside its network is
far more important on a day-to-day basis than its external
connectivity. Part of the trouble is that in the IETF, we don't think
much about that, since our attention is on global connectivity.
Also, NAT provides the ability to connect a small network to a service
provider that only provides a single DHCP address, or wants to charge
extra for every device you attach to its network. NAT is a
significant technical tool in the business conflict between user and
service provider.
Dale