You can turn off Internet sharing to allow bridging between the network’s wireless and wired computers. With bridging turned on, AirPort-enabled computers have access to all services on the Ethernet network. The wireless device doesn’t provide Internet sharing services.
Using the base station or a Time Capsule as a bridge can address incompatibilities between the wireless device’s Internet sharing features and your ISP’s connection method.
If you connect to the Internet using PPPoE, you can’t set it up as a bridge. When your base station is using PPPoE, it’s acting as a router and distributes IP addresses to clients on the network using DHCP and NAT.
Open AirPort Utility, located in the Utilities folder in the Applications folder on a Mac, and in Start > All Programs > AirPort on a Windows computer.
Select your wireless device and click Manual Setup. Enter the password if necessary.
Click Internet in the toolbar, and then click Internet Connection.
Choose Off (Bridge Mode) from the Connection Sharing pop-up menu.