Every week we post TCP/IP, subnetting, and other networking certification questions to help you prep for the exams.

Which of the following IP subnet masks allows for up to 30 hosts per subnet?

1. 255.255.255.0
2. 255.255.255.128
3. 255.255.255.192
4. 255.255.255.224

The answer is D.

If you use the formula 2ⁿ=x where x=hosts and n=remaining zeros in the last octet, you see that 255.255.255.224 is 11111111111111111111111111100000 in binary, and there are five zeros remaining. So: 2⁵−2=30.

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