How many addresses are in a /28?

• A. 16
• B. 8
• C. 32
• D. 64

Answer: (A)

In CIDR notation, the number after the slash shows how many bits are fixed for the network; the remaining bits are for hosts. A /28 leaves 4 host bits (32 minus 28). With 4 bits, you can form 2^4 = 16 addresses in that subnet. So there are 16 addresses total in a /28. If you’re counting usable devices, subtract the network and broadcast addresses, giving 14 usable hosts. The other options correspond to 3, 5, or 6 host bits (8, 32, or 64 addresses), which is why they’re not correct for a /28.