In order to enjoy a multiplayer game in Close Combat - Wacht am Rhein you might have to open the following ports for the other players to be able to join:
UDP 2302 - 2400
The instructions below might help:
When hosting please make sure to send that port to your friend.
Next share your ip address.
Should the IPv4 address not work please use the following:
When hosting make sure you use the port you have opened.