IP Addressing

The Internet consists of many pieces of equipment to connect all of the computers together. Servers, workstations and routers are just some types of equipment that makeup the Internet. These pieces of equipment, as well as others, will be examined in other chapters. Each piece of equipment on the Internet must have a unique address to identify itself from the thousands of other items on the Internet. This unique numeric address is known as an IP Address.

1 Main Street
Garden City, New York 11530

Above is a standard postal address. The 1 represents a residence on the street Main Street. There can be more than one house in the United States with the number 1 and more than one house on Main Street. There are many houses in Garden City, and of course in the state of New York. A residential address, in its entirety, represents a single unique location the world. For the same reason of identifying a single location for the transmission and reception of information, every item on the Internet must have a unique address.

An IP address is comprised of four numbers separated by periods, known as a four-byte dotted notation. This address is in the form of w.x.y.z, where each variable represents a numerical value in that particular position.

When analyzing an IP address, the first item to determine is the class for an address. The very first byte indicates the class. In an address of 198.38.12.2, the 198 is the first byte and represents the class. The breakdown of the class assignments is indicated below.

Class Range

A 1 - 127

B 128 - 191

C 192 - 223

D 224 - 239

E 240 - 255

Since the first byte of 198 falls within the range of 192 - 223, the IP address of 198.38.12.2 is a class C address. Discussed later will be the differences of the classes.

An address is comprised of two parts, a network portion and a host portion. For a class A address, the first byte is considered the network and the last three bytes are the host portion. For a class B address, the first two bytes represent the network portion and the last two bytes represent the host. Finally, for a class C address, the first three bytes represent the network and the last byte represents the host. The figure below clarifies this representation.

Regardless that a range has been assigned for both class D and E IP addresses, there are no official unique class D and E addresses in existence. These addresses are being reserved for future growth of the Internet addressing scheme.

The network portion for a particular network is a fixed value and the host portion values can range from 0 - 255, giving 256 values in each node byte.

Notice in the above examples that the network address of 112 is consistent for each of these systems and the host portion is different. Again, the combination of the network and host portion for a system is a unique IP address.

If a class A system has three positions for the host portion and each position can have 256 values in it, then a class A system can have 16,777,216 possible hosts. This is calculated by 256 x 256 x 256 or 256³ (256 values in three positions). A class B address has two host positions and therefore a total of 65,536 nodes. A class C address has only one host position and therefore can only have a maximum of 256 nodes on that network. The chart below indicates the difference in the classes for both the amount of networks and hosts per class.

It is obviously advantageous for a company to be assigned a class A address and have 16,777,216 address at their disposal. Some class C companies can overcome some of the difficulties of being limited to only 256 hosts by obtaining multiple class C addresses.