What is the Class A address format?

• A. The first byte is the network address, followed by three bytes for host addresses.
• B. The first two octets are network, last two are host.
• C. It uses four bytes for the network, none for host.
• D. It uses a 24-bit network portion.

Answer: (A)

In Class A addressing, the network portion is 8 bits and the host portion is 24 bits. That means the first octet defines the network, and the remaining three octets define hosts within that network. So the format is one byte for the network, followed by three bytes for the host addresses. The first bit of that first octet is 0, placing Class A networks in a range from about 1.0.0.0 up to 126.0.0.0 (with 0.0.0.0 and 127.0.0.0/127.0.0.1 reserved for special uses). This aligns with the statement that the first byte is the network address, followed by three bytes for hosts. The other descriptions mix up where the network and host portions reside: for example, two bytes for the network and two for the host describes Class B; having four bytes for the network and none for hosts isn’t how IPv4 addressing is organized; and a 24-bit network portion corresponds to Class C, not Class A.