The Router's MAC address is a 12-digit code assigned for identification, like a social security number. Some ISPs require that you register a MAC address. Input this MAC Address to MAC Address field or press the Clone button and click the Save Settings button. To use the Clone button, the computer viewing the Web-utility screen will have the MAC address automatically filled in the MAC Address field.  This 'clones' your network adapter's MAC address onto the  Router, and prevents you from having to call your ISP to change the registered MAC address to the Router's MAC address. The MAC address assigned will be the one who viewed the User interface.