Transmission Control Protocol/Internet Protocol (TCP/IP) defines the rules computers must follow to communicate with each other over the Internet. TCP is the primary Internet protocol for the reliable delivery of data. IP provides an addressing structure that is responsible for delivering data from the source computer to the destination computer.

An IP address is a number that is used to identify a device on the network. Each device on a network must have a unique IP address to communicate with other network devices. As noted earlier, a host is a device that sends or receives information on the network. Network devices are devices that move data across the network.

A person's fingerprints usually do not change. They provide a way to physically identify people. The mailing address of a person can change, as it relates to where the person lives or picks up mail. This address can change. On a host, the Media Access Control (MAC) address is assigned to the host NIC and is known as the physical address. The physical address remains the same regardless of where the host is placed on the network, in the same way that fingerprints remain with the person regardless of where the person goes. MAC addresses consist of 6 groupings of 2 hexadecimal values separated by either a dash (-) or a colon (:), for example, 00-26-6C-FC-D5-AE. Hexadecimal values are defined as a range of the numbers from 0-9 and the letters a-f.

The IP address is similar to the mailing address of a person. It is known as a logical address because it is logically assigned based on the host location. The IP address, or network address, is based on the local network and is assigned to each host by a network administrator. This process is similar to the local government assigning a street address based on the logical description of the city or village and neighborhood.

IPv4 and IPv6

In the early 1990s there was a concern about running out of IPv4 network addresses, which lead the Internet Engineering Task Force to begin looking for a replacement. This led to the development of what is now known as IPv6. Currently IPv6 is operating alongside and is beginning to replace IPv4.

An IPv4 address consists of 32 bits with a potential address space of 2^32. In decimal notation that is approximately a 4 followed by 9 zeroes, an IPv6 address consists of 128 bits with a potential address space of 2^128. In decimal notation, that is approximately a 3 followed by 38 zeroes. With IPv6, the number of addresses available per person is approximately 10^30. If the IPv4 address space is represented by a marble, then the IPv6 address space is represented by a sphere that is almost the size of the planet Saturn.