Subnetting Practice Quiz
Calculators check your work - this quiz builds the skill. Every question is generated fresh: a random private IPv4 address and prefix, asking for the network address, broadcast address, first or last usable host, usable host count or dotted subnet mask. Practice mode is untimed and shows a worked solution for every question; Timed mode gives you 10 questions at 60 seconds each, like real exam pressure.
How the worked solutions think
Every solution uses the same block-size method: host bits = 32 - prefix, block size = 2^host bits, and subnets start at multiples of the block size in the interesting octet. The broadcast address is the last address of the block, and usable hosts are everything strictly between network and broadcast. Learn the method step by step in our guide: How to Subnet IPv4 in Under a Minute.
Stuck on a question? Check it with the subnet calculator, or design whole multi-subnet plans with the VLSM calculator - then come back and drill until the answers are instant.
Subnetting is guaranteed marks on CCNA and Network+
When you can subnet in your head, the rest of the exam gets easier. Measure yourself with the free 30-question samples for CCNA 200-301 and Network+ N10-009.
Free CCNA SampleFree Network+ SampleFAQ
How can I get faster at subnetting?
Speed comes from the block-size method: for any prefix, the block size is 2^(32 - prefix), subnet boundaries are multiples of the block size in the interesting octet, and the broadcast address is always one less than the next boundary. Drill one question type at a time in Practice mode, read the worked solutions, then switch to Timed mode to build exam pace.
What is the block size of a /27 subnet?
A /27 leaves 5 host bits, so the block size is 2^5 = 32 addresses: subnets start at 0, 32, 64, 96 and so on in the last octet, and each /27 has 30 usable hosts.
Why does the usable host count subtract 2?
Every subnet reserves its first address as the network address and its last address as the broadcast address, so usable hosts = total addresses - 2. A /26 has 64 total addresses and 62 usable hosts.
What is the difference between Practice mode and Timed mode?
Practice mode is untimed and shows a full worked solution after every answer. Timed mode gives you 10 questions at 60 seconds each and reports your score and best streak at the end - use it to rehearse real exam pressure.