Three Network Classes
In a 32-bit IP address, the number of bits used to identify the network and the host vary according to the network class of the address. In a Class C network, the first 3 bits, or the high-order bits, are always "110." The next 21 bits are used to define the Class C network, and the final eight bits are used to identify the host. The IP address is represented in dotted decimal notation of four 8-bit fields, or octets, that have been converted from binary to decimal numbers. The following refers to "decimal numbers".
Class C Networks
This is the most widely used class by small businesses. When you look at the IP address, you'll notice that class C networks start with a first number that's between 192 and 223 (205.161.74.x for example). There can be up to 2,097,151 class C networks and each network can handle close to 254 computers.
Class B Networks
IP addresses of this type starts with a number between 128 and 191. It's possible to have 16,384 of these networks and each class B network can handle up to 65,534 IP addresses or computers.
Class A Networks
Starts with a number between 1 and 126. Only 126 of these networks are available, however each class A network can handle 16,777,214 IP addresses or computers.
