Which class would you use to maximize the number of networks in classful addressing?

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

Answer: (A)

In classful IPv4 addressing, the number of networks you can have depends on how many bits are reserved for the network portion. The more bits allocated to networks, the more networks you can create, though that reduces how many hosts you can address per network.

For Class C, addresses begin with 110, which fixes the first three bits of the first octet. That leaves 5 bits in the first octet plus all 8 bits in the next two octets for the network number, giving 21 bits total for the network. That yields 2^21 possible networks (2,097,152). This is far more than Class B (2^14 networks) or Class A (2^7 networks). Class D is used for multicast and isn’t counted in the same way for unicast networks.

So, to maximize the number of networks in classful addressing, you use Class C.