The NAT type listed on the Multiplayer Menu is for your connection to the hosting service. In order to effectively connect as Open you must first set your console as the DMZ host using the admin options on your router or modem. In addition, you must setup your router or modem to forward information on the following ports to your console:
  • 81, 3074, 3075, 3478, 3479 UDP (User Datagram Protocol)
  • 80, 443, 3074, 5223 TCP (Transmission Control Protocol)
  • 27000-27050