CompTIA Network+ (N10-009) — Question 435

An administrator needs to configure an IoT device with a /21 subnet mask, but the device will only accept dotted decimal notation. Which of the following subnet masks should the administrator use?

Answer options

• A. 255.255.224.0
• B. 255.255.240.0
• C. 255.255.248.0
• D. 255.255.252.0

Correct answer: C

Explanation

The correct subnet mask for a /21 is 255.255.248.0, which corresponds to the binary representation of 21 bits set to '1'. Options A, B, and D represent /19, /20, and /22 subnet masks respectively, which do not match the required /21 configuration.