How many total addresses and how many usable hosts are in a /28 subnet?

• A. 16 total addresses, 14 usable.
• B. 256 total addresses, 254 usable.
• C. 8 total addresses, 6 usable.
• D. 32 total addresses, 30 usable.

Answer: (A)

A /28 subnet has 4 host bits (32 − 28 = 4), so there are 2^4 = 16 total addresses. In IPv4 subnets, the network address (all host bits zero) and the broadcast address (all host bits one) aren’t assignable to hosts, leaving 16 − 2 = 14 usable host addresses. The other options reflect different subnet sizes (for example, a /24 has 256 total and 254 usable, a /29 has 8 total and 6 usable, a /27 has 32 total and 30 usable). So the correct result is 16 total addresses and 14 usable.