Connect to the Internet using a static IP address in AirPort Utility on Mac
When you use AirPort Utility Setup Assistant to set up your new base station or extend an existing network, it automatically configures the best settings for your network. It’s recommended that you manually configure your base station’s settings only if instructed to do so by your ISP or network administrator.
That said, if your ISP gave you an IP address with your account, as well as other information such as a subnet mask and router address, you can manually configure your base station to connect to the Internet using a static IP address.
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. You may need to enter a password for the base station.
Click Internet, click the Connect Using pop-up menu, then choose Static.
Enter the following information from your ISP:
An IPv4 Address
A subnet mask
A router address
At least one DNS or IPv6 DNS server address
Important: Don’t modify the Domain Name field unless you’re instructed to do so by your ISP or network administrator.
Click Update to save your changes.