You can set up a computer on your AirPort network as a default host so that this computer will be exposed to the Internet and receive all inbound traffic. This may be useful if you use a computer on your AirPort network to play network games, or if you want to route all Internet traffic through a single computer.
Your base station or your Time Capsule needs to be set up to share its Internet connection using Dynamic Host Configuration Protocol (DHCP) and Network Address Translation (NAT).
Open AirPort Utility, located in the Utilities folder in the Applications folder on a computer using Mac OS X, and in Start > All Programs > AirPort on a Windows computer.
Select the device you’re setting up, and then click Manual Setup. Enter the password if necessary.
Click Internet in the toolbar, and then click NAT.
Select "Enable Default Host at" and assign the IP address to the computer on your network you want to set up as the default host. The default address is 10.0.1.25.