Under the Endpoints menu hover over Endpoint Management, then select Endpoint Groups. Then on the upper right side of the new page select the add group button. Select create new from the menu that pops up. In the filter box search for IP Address. If you choose IP Address = then you can use CIDR notation (IE 10.0.0.1/24 or 10.0.0.1/16) or you can select IP Address Range, this will allow you to input a specific range of IP addresses.