1-1
1 IP Addressing Configuration
IP Addressing Overview
IP Address Classes
IP addressing uses a 32-bit address to identify each host on a network. An example is
01010000100000001000000010000000 in binary. To make IP addresses in 32-bit form easier to read,
they are written in dotted decimal notation, each being four octets in length, for example, 10.1.1.1 for the
address just mentioned.
Each IP address breaks down into two parts:
z Net ID: The first several bits of the IP address defining a network, also known as class bits.
z Host ID: Identifies a host on a network.
For administration sake, IP addresses are divided into five classes, as shown in the following figure (in
which the blue parts represent the address class).
Figure 1-1 IP address classes
Table 1-1 describes the address ranges of these five classes. Currently, the first three classes of IP
addresses are used in quantity.
Table 1-1 IP address classes and ranges
Class Address range Description
A 0.0.0.0 to 127.255.255.255
Address 0.0.0.0 means this host no
this network. This address is used by a
host at bootstrap when it does not
know its IP address. This address is
never a valid destination address.
Addresses starting with 127 are
reserved for loopback test. Packets
destined to these addresses are
processed locally as input packets
rather than sent to the link.
B 128.0.0.0 to 191.255.255.255 ––
C 192.0.0.0 to 223.255.255.255 ––
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