IP (Internet Protocol) -- The Internet Protocol, or IP, is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite. IP is a routing protocol that determines the best "route" or "path" for information to

travel between stations (PC workstations, file servers, or routers). Setting up and understanding IP routing can be easy for small, less-complex networks or complicated for large, dissimilar networks. The key to understanding IP routing is to understand its most complex and flexible component--IP addressing.

Understanding IP addressing

IP addressing is a way to identify stations or hosts on a network. An IP address is a unique 32-bit number that uses a format of 4 bytes, divided into four 8-bit parts, with each byte separated by a decimal point (called dotted decimal notation). Each byte can be a number from 1 to 255. For example, 131.9.1.2 is a valid IP address. By having unique addresses on a network, you can identify individual stations (also call hosts) on the single network.

An IP address consists of two parts-one part identifies the network, and one part identifies the node. Nodes define connected devices on a network, and they define network users and PCs.

You can assign IP addresses inside private companies using arbitrary addresses. But if you want to connect to the internet, you must use registered IP addresses that conform to an international standard. IP addresses are assigned by software; they are not assigned to equipment at the factory as are Ethernet and token ring adapters.

There are five types of IP addresses. Three are associated with networks. They are:

Class A addresses are for networks that have a large number of hosts, up to a maximum of 16, 777, 216 on a single IP network. The first octet (that is the first 4 bytes, or the first segment before a decimal) is between 1 and 126. (127 is reserved for loopback and is used for internal testing on the local machine.)

Class B addresses are for medium-sized networks. The first octet is between 128 and 191.

Class C addresses are for small networks, with up to 255 hosts. The first octet is between 192 and 223.

Class D addresses are reserved for multicasting and the first octet is between 224 and 239. Class E addresses (240 to 255) are reserved and should not be used.

The three network IP address classes (A, B, and C) are different because each byte in the IP address class is associated with a network or host ID. The following illustration shows the differences, in byte assignments, between the three address classes.

Notice that Class B and Class C addresses have fewer host ID bytes and more network bytes than Class A. This allows a single Class A network to have more addresses for the single network.