What is an IP Address?

If you want to connect to another computer, transfer files to or from another computer, or send an e-mail message, you first need to know where the other computer is - you need the computer’s “address.” An IP (Internet Protocol) address is an identifier for a particular machine on a particular network; it is part of a scheme to identify computers on the Internet. IP addresses are also referred to as IP numbers and Internet addresses. An IP address consists of four sections separated by periods.

Each section contains a number ranging from 0 to 255. Example = 198.41.0.52 These four sections represent both the machine itself, or host, and the network that the host is on. The network portion of the IP address is allocated to Internet Service Providers (ISPs) by the InterNIC, under authority of the Internet Assigned Numbers Authority (IANA).  ISPs then assign the host portion of the IP address to the machines on the networks that they operate.

Which sections of the IP address represent the network and which sections represent the machine will depend on what “class” of IP address is assigned to a network. There are 5 classes of IP addresses: Class A, Class B, Class C, Class D, and Class E. Classes correspond either to the size of the network (the number of hosts that the network can support) or are reserved for specific purposes, such as multicasting and experimentation. The diagram below compares Class A, Class B and Class C IP addresses.

The blue numbers represent the network and the red numbers represent hosts on the network. Therefore, a Class A network can support many more hosts than a Class C network. IP addresses are unique. No two machines can have the same IP number. IP addresses are also global and standardized. All machines connected to the Internet agree to use the same scheme for establishing an address.