Direct network traffic in AirPort Utility on Mac
If you need to ensure that requests are routed to your web or FTP server, or to a specific computer on your network, you need to establish a fixed IP address for the server or computer and provide inbound port mapping information to the base station. You can set up a fixed IP address by configuring a DHCP reservation on the base station, or by configuring TCP/IP manually on the computer whose ports you’re mapping.
Open the AirPort Utility app on your Mac, located in the Utilities folder in the Applications folder.
In the graphical overview, select the base station you want to configure, then click Edit. Enter the password for the base station.
Click Network, then verify that “DHCP and NAT” is selected in the Router Mode pop-up menu.
Click the Add button below the Port Settings list, then do one of the following in the dialog that appears:
Choose IPv4 Port Mapping, enter the IP address in the Private IP Address field, then choose a predefined service from the Description pop-up menu.
Note: If a predefined service is not available, enter custom port numbers in the appropriate field or fields, then type a description in the Description field.
Choose IPv6 Firewall Entry, then enter the IPv6 address in the IPv6 Address field. Then choose to allow all services and ports through the firewall or choose to specify which ports to allow through the firewall. If you choose specific ports, enter the port numbers in the TCP Port and UDP Port fields.
Click Save to save your changes and close the dialog, then click Update to save the changes.