Quick Reference Guide

Reference Guide for the Model RT338 ISDN Router
1-8 Introduction
There are five standard classes of IP addresses. The address classes determine the network and host
sections of the address differently. Address classes allow for different numbers of hosts on a
network. Each address type begins with a unique bit pattern, which is used by the TCP/IP software
to identify the address class. After the address class has been determined, the software can
correctly identify the host section of the address. The three main address classes are illustrated in
Figure 1-1, which shows the network and node sections of the address for each address type.
Figure 1-1. Three Main Address Classes
IP address classes are described in Table 1-1.
Table 1-1. Address Classes
Address
Class
Range Description
A 1.x.x.x to 126.x.x.x Class A addresses can have up to 16,777,214 hosts on a single network.
They use an 8-bit network number and a 24-bit node number.
B 128.1.x.x to
191.254.x.x
Class B addresses can have up to 65,354 hosts on a network. They use a
16-bit network number and a 16-bit node number.
C 192.0.1.x to
223.255.254.x
Class C addresses can have 254 hosts on a network. They use 24 bits for
the network address and 8 bits for the node.
D 224.0.0.0 to
239.255.255.255
Class D addresses are used for multicasts (messages sent to many hosts).
E Class E addresses are for experimental use.
7261
Class A
Network Node
Class B
Class C
Network Node
Network Node