see the web articles : http://aftab-tekdad.hubpages.com/hub/ip-tutorial-subnetting http://www.wikihow.com/Calculate-Network-and-Broadcast-Address http://www.linglom.com/2007/02/20/how-to-find-subnet-number-ip-addresses-in-the-subnet-in-a-few-seconds/ http://www.aboutmyip.com/AboutMyXApp/SubnetCalculator.jsp http://www.iplocation.net/tools/netmask.php Hope this helps and explains