User`s guide

178 Appendix E Understanding IP Addresses and Subnet Masking
The following example shows an octet conversion when not all of the bits are set to 1:
0 1 0 0 0 0 0 1
0 64 0 0 0 0 0 1
(0+64+0+0+0+0+0+1=65)
The following example shows an IP address represented in both binary and decimal notations:
decimal
192. 168. 1. 1
binary 11000000 10101000 00000001 00000001
An IP address consists of two components, the network address and the host address.
 The network address always contains the first octet. It is used to identify the network to
which a computer belongs.
 The host address identifies the particular computer host (or “node”) on the network. The
host address always contains the last octet.
If you take the example 192.168.1.1 and divide it into these two parts you get the following:
Network
192. 168. 1.
Host 1
or
Network
192. 168. 1. 0
Host 0. 0. 0. 1
E.2 Network Classes
The octets serve a purpose other than simply separating the numbers. They are used to create
classes of IP addresses that can be assigned to a particular business, government, or other entity
based on size and need. There are five different classes of networks, designated A, B, C, D, and
E. This appendix describes classes A, B, and C, since classes D and E are reserved and beyond the
scope of this appendix.
 Class A - supports 16 million hosts on each of 126 networks
 Class B - supports 65,000 hosts on each of 16,000 networks
 Class C - supports 254 hosts on each of 2 million networks
The class of an IP address can be determined from the three high-order bits. Figure E-1 shows the
significance in the three high-order bits and the range of addresses that fall into each class.