Subnetting is how IP addresses range and how IP address classes are determined. On the surface, it may seem complicated, but anyone familiar with IP addresses or binary numbering systems should have no problem understanding how it works. If you are unfamiliar with either or both of these topics, the overview below should be sufficient to give you a basic understanding of the concept.
As computers use binary numbering (1s and 0s) in groups of 8 (a byte) instead of consecutive numbering like people do, it is necessary to understand how binary numbers work.
Take a moment to look at the following sequence: 128, 64, 32, 16, 8, 4, 2, 1 Notice that there are 8 numbers. These form the information for 1 byte of binary in a way that the human brain can understand.
How does it work? 1 is the "on" number and 0 is the "off" number. So, if the computer sees a 1111111, you should add all the numbers in the above sequence (255). If the binary number were 11010100, you would add the numbers that correspond with the 1s, that is, 128, 64, 16, and 4 (192). For the average home user, no more understanding than that is required.
IP addresses come in four classes, that is, A - D. Notice that there are four fields is a subnet. The full or 255 fields define the class of network and the host. The remainder are the network addresses. A home network is almost always a class C IP address, 192.168.0.1 specifically. The subnet mask is 255.255.255.0. For a class A and B address, the subnet would be 255.0.0.0 and 255.255.0.0 respectively. Again, for most users, no more understanding than that is required.
IP addressing and subnetting The standard class C home network results in a default subnet mask of 255.255.255.0. This gives a large network. If you want to divide that network into subnets, you simply have to "borrow" from the network section of the subnet by changing a 0 to a 1. The number of subnets and addresses can be figured out manually or by using the free subnet calculator on sites such as Subnet-calculator.com or Subnetmask.info.