Page 94 - M. Abrahim Thesis

Chapter (4) Network Design

Figure 4-12 shown a Class A Address Scheme

The first bit of a Class A address is always 0. With that first bit a 0, the lowest number that
can be represented is 00000000 (decimal 0), and the highest number that can be represented is
01111111 (decimal 127). However, these two numbers, 0 and 127, are reserved and cannot be used
as a network address. Any address that has a value between 1 and 126 in the first octet is a Class A
address.

4.2.3.2 Class B Addresses

The Class B address, shown in Figure 4-13, was designed to support the needs of moderate-
to large-sized networks. A Class B IP address uses two of the four octets to indicate the network
address. The other two octets specify host addresses.

Figure 4-13 shown a Class B Address Scheme

The first 2 bits of the first octet of a Class B address are always 10. The remaining 6 bits may
be populated with either 1s or 0s. Therefore, the lowest number that can be represented with a Class
B address is 10000000 (decimal 128), and the highest number that can be represented is 10111111
(decimal 191). Any address that starts with a value in the range of 128 to 191 in the first octet is a
Class B address.

4.2.3.3 Class C Addresses

The Class C address, shown in Figure 4-14, is the most commonly used of the original address
classes. This address space was intended to support a lot of small networks.

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