Your computer has a private IP address, while your U-verse router maintains a shared public IP address. When you send data to the Internet, the router replaces your private address with the public address and a port number. When data comes back, it puts the private address back and routes the data. If it didn't assign the port number, it drops the data. This process is called Network Address Translation, and it creates a natural firewall. If you're playing a game that communicates over a specific port, you must open the port, which tells the router not to perform NAT and to send all Internet traffic on the port directly to your computer.
Launch a browser, type "http://homeportal/" and press "Enter" to navigate to the AT&T U-verse home portal page on your AT&T U-verse router.
Click "Go," and then click the "Settings" tab. Click the "Broadband" tab inside the Settings tab.
Click the "Firewall" tab inside the Broadband tab, and then choose "Applications, Pinholes and DMZ."
Identify the computer to which you want to forward data on the port, and choose the computer from the list of network devices it displays. Select "Allow Individual Application(s)" in the Edit Firewall Settings section.
Select the application for which you need the open port if it's in the list of applications that AT&T U-verse can configure for you automatically, and then click "Add."
Choose "Add a New User-defined Application" if your application is not in the list or if you're opening the port for a device. Type the name of the application in the Application Profile Name field. Select either "TCP" or "UDP" for the protocol according to your instructions. Type the port number you want to open in both the "From" and "To" fields, or type the beginning of a port range in the "From" field and the ending port number in the "To" field. Type "8400" in the Protocol Timeout field if you selected TCP, or type "600" if you selected UDP. Leave the "Map to Host Port" field blank unless your instructions require a different public and private port.
Click "Add to List." Repeat the process if you need to open more than one non-consecutive port or the same port with a different protocol.
Click "Back" when you've finished opening the ports in NAT. Click "Save" to save your changes and reboot the AT&T U-verse router.
AT&T provides the following disclaimer: "Opening ports in the modem firewall can leave your computers exposed to malicious attacks. AT&T is not responsible for potential attacks made to your computer systems or damage resulting from an attack caused by opening a port."