Subnetting practice trainer
Subnetting is a skill of repetition. This trainer generates new questions without limit, checks your answer at once and shows the working, so you can see which step went wrong. Pick one question type to drill a weak spot or use mixed mode.
How to work a question quickly
- Write the prefix as a mask. A /26 leaves 6 host bits, so the last octet changes in steps of 64 (256 − 192).
- Find the block: the network address is the largest multiple of the block size that is not above the address.
- The broadcast address is the next block start minus 1. The usable range lies between the network and broadcast addresses.
- Usable hosts are 2^host bits − 2. A /31 (point-to-point, RFC 3021) has 2 usable addresses and a /32 is a single host.
Worked example. For 192.168.4.77/26 the block size is 64, so the network is 192.168.4.64, the broadcast address is 192.168.4.127, the first host is .65, the last host is .126 and there are 62 usable hosts.
The full method, with more examples, is in subnetting step by step. Exams that test it include CCNA 200-301 and Network+ N10-009; written questions are in the subnetting practice questions.