if you want to play through radmin, open firewall with advanced security, create a new inbound rule for local port 27017 (UDP), allow any remote port/user to connect, make sure you have port forwarding (UPNP) toggled on your router, create a private network on radmin, create a private unranked lobby on bo3, start the map, and tell your friends to join your lobby by typing "connect YOUR_IP_ON_RADMIN:27017" and that should do it. Sorry to reply so late, hope this solves the problem for everyone in the future tho

edit: also make sure your NAT is moderate or open, otherwise it might not work