Use Gigabit Ethernet on Mac
If your Mac supports it, you can use Gigabit Ethernet, which requires a special Gigabit Ethernet cable.
If you don’t have a Gigabit Ethernet cable, you can still connect to a Gigabit Ethernet network by adjusting the Ethernet speed of your computer.
Note: Changing your network settings affects the way your computer interacts with your network. Unless your network administrator has given you specific settings, use the automatic settings. Entering the wrong settings can affect network performance.
On your Mac, choose Apple menu > System Settings, then click Network in the sidebar. (You may need to scroll down.)
Click your Ethernet service on the right, then click Details.
Click the Configure pop-up menu, then choose Manually from the pop-up menu.
Click the Speed pop-up menu, then choose a speed from the pop-up menu.
You can also adjust duplex and the maximum transmission unit (MTU) settings. Check with your network administrator for the settings specific to the network.