How to Find a Subnet Mask Numberby Andrew Todd ; Updated September 28, 2017
A subnet mask number is used to determine which part of an Internet Protocol (IP) address is used by the host, and which part is used by the network. A subnet mask, like an Internet Protocol address, consists of four groupings of numbers, separated by periods. For instance, a subnet mask will appear as “255.255.255.0.” Find your subnet mask number using the “ipconfig” command in your command prompt.
Open the Start menu.
Click “Run,” type “cmd” and click “OK” (if using Windows XP or earlier). If using Windows Vista or Windows 7, type “cmd” directly into the search box on the Start menu.
Type “ipconfig” in the command prompt, and press “Enter.” Your subnet mask will be displayed below your Internet Protocol address and will be labeled “Subnet Mask.”