How to Find My Gateway Address on a Mac
The default gateway is a network device like a router that your computer connects to in order to connect to the network (and the Internet at large). Whenever you connect to a local network or the Internet, your computer finds the default gateway so that network communications can be carried out properly.
Start up your Mac and log in to the operating system.
Click on the Apple logo and then click on "System Preferences."
Click on "View" and then click on "Network."
Click on the network connection you are using and then click on the "Advanced" button. Your default gateway IP address is listed next to the "Router" label.