CompTIA A+ Core 1 (220-1201)NetworkingMedium
A technician is designing a subnet that must support at least 50 host devices while wasting as few IP addresses as possible. Which of the following subnet masks should the technician use?
- A255.255.255.192
- B255.255.255.224
- C255.255.255.240
- D255.255.255.128
Show answer & explanationAnswer & explanation
Correct answer: A. 255.255.255.192
A /26 mask (255.255.255.192) leaves 6 host bits, providing 2^6 - 2 = 62 usable addresses, which is enough for 50 hosts with minimal waste. A /27 (255.255.255.224) only provides 2^5 - 2 = 30 usable hosts, which is insufficient, while /25 (255.255.255.128) provides 126 hosts, wasting more addresses than needed.
Why the other options are wrong
- B. /27 provides only 30 usable hosts, not enough for 50 devices.
- C. /28 provides only 14 usable hosts, far too few.
- D. /25 provides 126 usable hosts, more than needed and wastes addresses.
Subnet Sizing (CIDR)
Subnet size is determined by host bits; usable hosts = 2^n - 2, where n is the number of host bits remaining after the mask.
- /26 = 62 usable hosts
- /27 = 30 usable hosts
- Choose smallest subnet that still meets host requirement to minimize waste
Memory trick: Subtract 2 for network/broadcast, then check if it fits.