SMAC uses Microsofts DirectPlay for internet connections (a component of DirectX).
According to Firaxis it uses no ports beyond those required by DirectPlay.
Directplay uses the following ports:
Initial TCP Connection: 47624 Outbound 47624 Inbound
Subsequent TCP Inbound : 2300-2400
Subsequent TCP Outbound: 2300-2400
Subsequent UDP Inbound : 2300-2400
Subsequent UDP Outbound: 2300-2400
To join a game you need 2300-2400 open plus 47624
To host a game behind a NAT router you need those ports mapped to the IP of the machine you are using.
The full article can be found here:
http://support.microsoft.com/support.../Q240/4/29.ASP
There is also more on firewall/proxy/router configuration
[This message has been edited by buster (edited March 28, 2001).]