?– The minimum decimal value for an octet is 0; it contains all 0s.
?– The maximum decimal value for an octet is 255; it contains all 1s.
While many computers might share the same network address, combining the network
address with a host address uniquely identi?¬?es any device connected to the network.
IP Address Classes
When IP was ?¬?rst developed, no classes of addresses existed, because it was assumed that
254 networks would be more than enough for an internetwork of academic, military, and
research computers.
As the number of networks grew, the IP addresses were broken into categories called
classes to accommodate different sizes of networks and to aid in identifying them. These
classes are illustrated in Figure 1-29.
Assigning IP addresses to classes is known as classful addressing. The allocation of
addresses is managed by a central authority, the American Registry for Internet Numbers
(ARIN), which you can go to at http://www.arin.net for more information about network
numbers.
Network
255
Dotted
Decimal
Maximum 255 255
128
64
32
16
8421
128
64
32
16
8421
128
64
32
16
8421
128
64
32
16
8421
255
1 1 1 1 1 1 1 1 Binary 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
172
Example
Decimal 16 122 204
1 89 16 17
32 Bits
24 25 32
1 0 1 0 1 1 0 0
Example
Binary 0 0 0 1 0 0 0 0 0 1 1 1 1 0 1 0 1 1 0 0 1 1 0 0
Host
IP Network Addressing 47
Figure 1-29 Address Classes
Five IP address classes are used, as follows:
?– Class A: The Class A address category was designed to support extremely large
networks.
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