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Computer Network 2021

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.

Figure 4-14 shown a Class C Address Scheme

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