>I'm curious, hich part of coda makes this not possible?

It is the rpc2's use of UDP and the need for a unique IP/port pair to
be unique computer.  If you have only one client behind a NAT box, you
can configure the NAT box to properly direct the rpc2 traffic to that
one box, but if you want 2 or more clients, you loose.  The NAT box
will have no clue to which client a UDP packet should be delivered.

If rpc2 was to change and use TCP, then the use of specific port
numbers on the client is no longer a problem and should then go
through NAT gateways.  This has been talked about, but not done.

-- 
Phil Nelson                       NetBSD: http://www.netbsd.org
e-mail: phil@cs.wwu.edu           Coda: http://www.coda.cs.cmu.edu
http://cs.wwu.edu/faculty/nelson