NAT problem understood

[theCoder]

I think...

After playing around trying to log into my brand new 0.3.0 install, here's what I've found.

The login server at eqlogin.eqemu.net tends to ignore the worldaddress (from the .ini file), if that's ever sent. It always reports back my external IP to my EQ client (confirmed through packet sniffing).

There are no problems with the EQEmu world or zone servers. At least as far as letting the users log in (I haven't gotten past that point yet). The world server, as far as I can tell, services login requests correctly. The problem is not what's being sent, or where it's being sent to, but where it's being sent from.

Here's what I see is happening:
1) The EQ client correctly gets my world server external IP address from the login server as X. It sends a login request to the world server at X.

2) The world server receives the request, processes it, and returns a response. Since the world server knows that the client is on the internal network, it uses the internal inteface (IP address Y) to send the response (actually, this is Linux's doing, but it's still right).

3) So far so good. But here's the problem. Everquest uses UDP to send data, which is a connectionless protocol. Because it's connectionless, applications that use it have to examine the source address of each packet to determine what the packet is for. So, when the EQ client sends a packet to IP X, it expects a response from X, not Y. I imagine (though I don't know for sure) that the the EQ client is just dropping the packets from IP Y, since it doesn't know that they're really from X.

So what are the solutions?

• Running your own login server is one solution, but it's not great. First, you can't do that, since even minilogin isn't being released anymore. Second, that means that you can't connect to the official login server. A stop-gap measure at best
  
• It would theoretically be possible to write a NAT module for EQEmu like the module for FTP. This module would fix the IP address so that it was the internal IP (Y) instead of the external IP (X). A little bit better solution, but hard to do (I don't even know where to start on that)
  
• Perhaps modify the world (and zone?) server so that it always says it's from IP in the send is X, even if it's using the internal interface. I don't know how much work this would entail. The downside to this approach is that it would most likely require that the server be run as root (I don't think normal users would be able to do this).
  
• Change the login server on eqlogin.eqemu.net to return the worldaddress field instead of the connection source. This would mean that external people couldn't play on my server (since my worldaddress is currently Y), but they can't anyway, since port 9000 isn't open externally.

Anyone have any other ideas? I'm not sure what else to do, and right now I can't even play on my own server. I'm going to try to look into the third option, since it seems the easiest for me to do (I think the fourth is the easiest, but I can't do that).