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160 A
PPENDIX
F: I
NTRODUCTION TO
IP A
DDRESSING
separated with dashes, for example,
1-408-555-1212
, IP
address number components are separated by decimal
points or dots (called
dotted decimal notation ), for
example,
123.45.67.89
. Because computers use a binary
number system, each number in the set must be less than
255.
There are three components that contribute to an IP
address:
■
IP address itself
■
Subnet mask
■
Default gateway
The following sections discuss each of these components in
detail.
IP Address
Just as each household or business requires a unique phone
number, a networked device (such as a computer, printer,
file server, or router) must have a unique IP address. Unlike
phone numbers, in IP addressing it is necessary to always
use the entire number when communicating with other
devices.
There are three classes of IP addresses: A, B, and C. Like a
main business phone number that one can call and then be
transferred through interchange numbers to an individual’s
extension number, the different classes of IP addresses
provide for varying levels of
interchanges or subnetworks
and extensions or device numbers. The classes are based on
estimated network size:
■
Class A — used for very large networks with hundreds
of subnetworks and thousands of devices. Class A
networks use IP addresses between
0.0.0.0
and
127.0.0.0
.
■
Class B — used for medium to large networks with
10–100 subnetworks and hundreds of devices. Class B
networks use IP addresses between
128.0.0.0
and
191.0.0.0
.
■
Class C — used for small to medium networks, usually
with only a few subnetworks and less than 200 devices.