Below are steps required to retrieve router IP address on Mac OS.

• Click on Apple icon in the left top corner of the screen
• In the menu click on "System Preferences..."
• You should see a window with System Preferences pop-up
• Click on "Network" icon in it. To quickly find this icon you can type its name in Search box
• Network window should pop up.
• Select active connection in it. It is marked with green circle
• Click on "Advanced..."
• In new Windows which will pop up select TCP/IP tab
• You should see a screen with data which will have "Router:" entry in it. This is your router IP address

Getting router IP address using terminal app.

• Click on Launchpad icon in the menu at the bottom of the screen
• Type Terminal in launchpad or find "Terminal" icon in a Launchpad icon list
• Click on "Terminal" icon
• In Terminal window type netstat -nr | grep default
• You should see a line of text appear. Look for an IP address of your router after "default" word. This is your router IP address