What are the valid host addresses in a Class A network?

• A. 10.0.0.1 through 10.255.255.254
• B. 10.0.0.0 through 10.0.0.255
• C. 10.255.255.0 through 10.255.255.255
• D. 10.0.0.1 through 10.0.0.254

Answer: (A)

In a Class A network, the default subnet mask is 255.0.0.0, so the first octet identifies the network and the remaining three octets identify the host. The network address for the 10.0.0.0/8 block is 10.0.0.0, and the broadcast address is 10.255.255.255. Any address between these two, excluding the network and broadcast addresses themselves, is a valid host address. That means valid hosts range from 10.0.0.1 to 10.255.255.254.

The listed options that include the network address (10.0.0.0) or the broadcast in the block, or that only cover a small subset of the 10.x.x.x space, aren’t the complete set of valid hosts. The full and correct range encompasses all addresses in the 10.0.0.0–10.255.255.254 span, excluding 10.0.0.0 and 10.255.255.255.