You to subnet is taking the network mask and sub-dividing it to have smaller IP ranges. A standard class C IP range is 192.168.1.0 with a subnet of 255.255.255.0 which you can see each dot lines up. A number (dot) a number(dot) ect... A 0 in the network mask or subnet mask means you can use all the numbers and that will be one range(block) of IP addresses with one broadcast address and one network address with many hosts. In my example of 192.168.1.0 here are the IP ranges. 192.168.1.0 Network IP 192.168.1.1-254 Host IP's 192.168.1.255 Broadcast address. 255.255.255.0 Subnet mask Notice how the numbers don't change if its a 255 in the subnet mask. To divide the IP range up you would need to change the subnet mask to something other then 255.255.255.0. Here is an example of dividing it in half. Group A 192.168.1.0 Network IP 192.168.1.1-126 Host IP's 192.168.1.127 Broadcast address. Group B 192.168.1.128 Network IP 192.168.1.129-254 Host IP's 192.168.1.255 Broadcast address. 255.255.255.128 Subnet mask for both groups. Here are two sites you could check out: This site explains more about subnetting in detail. http://www.learntosubnet.com/ This is just a simple subnet calculator after a while of networking you will be able to do it in your head just as fast. http://www.subnet-calculator.com/subnet.php