What is the structure of a Class A IP address?

• A. network.network.network.network
• B. network.host.host.host
• C. host.host.host.network
• D. host.network.host.host

Answer: (B)

In Class A addressing, the first 8 bits (the first octet) identify the network, and the remaining 24 bits (the last three octets) identify the host within that network. The default subnet mask is 255.0.0.0, so only the first octet is used to define the network, while the other three octets are available for host addresses. This makes the structure network.host.host.host.

That’s why the pattern with the first part as the network and the last three as the host parts—network.host.host.host—is the correct description. The other patterns would imply different allocations (for example, treating more than one octet as network or placing the host portion in the first octet), which doesn’t align with Class A’s 8/24 split.