1. Open Airport Utility, select the router that connects you to the Internet, and choose Manual Setup

2. Click on the Internet icon, and choose NAT, and check the Enable NAT Port Mapping Protocol box as shown below:

   

Troubleshooting

• If you don't see the NAT option when you choose the Internet icon, you need to make sure that your router is connected to the Internet, and that your Connection Sharing is set to share a public IP address as shown below:

  

• If you don't see the Connection Sharing option, that means that your AirPort isn't the router that connects you to the Internet. You may be setting up the wrong router. Or you're sure this is the correct router, you need to cick on the AirPort icon, choose Wireless, and make sure that the wireless mode is set to Create a wireless network