To accommodate 50 hosts per subnet, which prefix length should you choose?

• A. /27
• B. /28
• C. /26
• D. /25

Answer: (C)

The main idea is how many hosts a subnet can support based on its prefix length. In IPv4, the number of total addresses in a subnet is 2^(32 minus the prefix). Two addresses—network and broadcast—are typically not usable, so usable hosts = 2^(32 - prefix) - 2.

For 50 hosts, you need at least 2^(32 - prefix) - 2 >= 50. If the host portion is 5 bits, you get 32 total addresses, 30 usable — not enough. With 6 host bits, you get 64 total addresses, 62 usable — enough. Therefore the prefix length is 32 - 6 = /26. That gives 64 addresses total (62 usable), which comfortably accommodates 50 hosts. A /25 would also work but wastes more address space, so the smallest suitable prefix is /26.