Every computer needs to have the hardware address of the network adapter (MAC address) registered before it can connect to the wired ethernet network.
Step 1: Get the MAC address
On a Mac, go to the Apple Menu > System Preferences > Network > Ethernet > Advanced > Hardware
Step 2: Enter the MAC address into the ONYEN website.
Go to http://onyen.unc.edu and click on DHCP registration. Create a new registration. Put the computer name (CM076-01, for example) in the name field and the MAC address you found in step 1 into the MAC address field.