User manual

B-2 Addressing Scheme

IP Addressing Basics

There are three address classes in IP, ranging with addresses

ranges as follows: Class A - 0-127; Class B - 128 - 191; and Class

C - 192 - xxx.

IP addresses are 32 bits long and generally written in what is

called dotted decimal notation: four decimal values separated

by periods. For example, 192.77.203.5.

These 32 bits are structured very differently from IPX addresses,

in which you always have an 8 hex digit network number

followed by a 12 hex digit node address.

The same 32 bits can be divided in a number of different ways

to indicate networks and subnetworks of different sizes.

Imagine what would happen if the colon in the middle of an IPX

address could slide left or right in the address. Also, imagine

that the node addresses are no longer the physical addresses of

your network interface cards, but arbitrary numbers that are

mapped to those physical addresses later. You could then

accommodate varying network structures from a small number

of network segments with huge numbers of nodes to large

numbers of networks with only a few nodes.

In Figure 1 below, you can think of the line between NET ID and

HOST ID as the equivalent of the colon in an IPX address.

Notice that the position of this line is determined by the position

of the first zero bit in the address.

CLASS A

CLASS B

CLASS C

NET ID

0 1 2 3 4

HOST ID

Figure 1. Address Class Map