For D-Link routers, go to Advanced/Applications, and enter these things in the fields, and click apply:
If you can't see the image:
1) Select "enabled".
2) (optional) Enter "Outpost II Multiplayer" or similar in the "name" field.
3) In the first field in "trigger port", put in 47776. In the second field, put 47807.
4) Select "UDP" in "trigger type".
5) Type in "47776-47087" in "public port".
6) Select "UDP" in "public port".
7) Click "Apply".
Note: This will allow you to join games, but not host outside of your LAN.