An AirPort Base Station or a Time Capsule can share a single Internet connection among several computers. The base station or Time Capsule can provide IP addresses and route Internet information to computers on the AirPort network 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 Internet Connection.
Choose "Share a public IP address" from the Connection Sharing pop-up menu.
Click DHCP and choose an address range from the DHCP Range pop-up menu. By default, the device uses the address range 10.0.1.2 to 10.0.1.200.
You can also set other DHCP options, such as how long a client computer receives a valid IP address, reserving specific IP addresses for specific client computers and more.
For more information about using DHCP on your network, click the link below.