I tried playing with a distant friend both with vikings addon installed(don't think that should matter, but maybe it does), and it worked:
one should be the server, the other should log in at ip.
for the server:
- open port 5479 on your router and forward it to your internal ip. (if you use a router)
- allow the port or the executable in your firewall. (you do have one do you?)
- tell your friend your external ip adress (find out:
https://www.google.com/search?q=whats+my+ip).
- start the game, go to multiplayer and choose 'lan' followed by 'create game'.
- setup map and conditions, wait in the lobby for your other player(s) to log in.
for the client:
- start the game, go to multiplayer and choose 'direct ip adress'.
- use the ip provided by the server (no need to specify port, just ip) and press join.
both once in:
- to signal you are ready to start start place a mark at ready (above your color) and off you go.
Hope you get it working,
Darkje