Which class has the smallest total number of networks in classful addressing?

• A. Class A
• B. Class B
• C. Class C
• D. Class D

Answer: (A)

In classful addressing, how many networks exist depends on how many bits are dedicated to identifying the network. For Class A, the first bit is fixed as 0, leaving 7 bits to identify the network. That yields 2^7, which is 128 possible networks. For Class B, the first two bits are fixed as 10, leaving 14 bits for the network portion, giving 2^14 (16,384) networks. For Class C, the first three bits are fixed as 110, leaving 21 bits for the network portion, giving 2^21 (2,097,152) networks. Class D is used for multicast and doesn’t follow the same network-count pattern as the other classes. Since 128 is the smallest, Class A has the smallest total number of networks.