Each TCP/IP host is identified by a logical IP address. The IP address is a network layer address and has no dependence on the data link layer address (such as a MAC address of a network interface card). A unique IP address is required for each host and network component that communicates using TCP/IP.

The IP address identifies a system's location on the network in the same way a street address identifies a house on a city block. Just as a street address must identify a unique residence, an IP address must be globally unique and have a uniform format.

Each IP address includes a network ID and a host ID.

Note The use of the term network ID refers to any IP network ID, whether it is class-based, a subnet, or a supernet.

An IP address is 32 bits long. Rather than working with 32 bits at a time, it is a common practice to segment the 32 bits of the IP address into four 8-bit fields called octets. Each octet is converted to a decimal number (the Base 10 numbering system) in the range 0-255 and separated by a period (a dot). This format is called dotted decimal notation. Table 10 provides an example of an IP address in binary and dotted decimal formats.

Figure 3 The IP address

The above notation w.x.y.z is used when referring to a generalized IP address.