The NAT patch was written so that people didn't have to change any DNS entries. However, it will
only work if and only if the world and zone servers are running on the NAT server. The NAT patch makes the EMU listen on only the external interface (actually, whichever interface you specify, but you want the external one). NAT servers have to have at least two interfaces, but the login server can only record and give out one of those. If the world server specifies to the login server that it is on the internal one, external clients cannot connect. If the world server says it's on the external interface, internal EQ clients get confused because of how the UDP packets are returned when the EMU listens on both interfaces. By forcing the EMU to only listen on the external interface, the UDP packets get formed the way the EQ client expects them and everything works.
What the NAT patch won't help with is an EMU server
behind a NAT server. The only way I know of to solve that is with port forwarding on the NAT server and DNS work on the EQ clients (note that you shouldn't need to mess with the hosts file on the NAT server).
A better solution would be to have a separate entry in the conf file specifying the bind address the EMU should use (0.0.0.0 will bind to all interfaces). As soon as I get some time (I'm in the midst of moving across the country right now, so I shouldn't even be reading this board
), I'm going to look into that, and also look into setting up autoconf and making a more "linux friendly" version.