Subnetting Practice
Free, unlimited IPv4 subnetting questions with instant, step-by-step worked answers. Built for CCNA, CompTIA Network+ & Security+ students. No signup.
$9
Subnetting Mastery Kit — a printable 1-page cheat sheet (masks, magic-number method, powers of two) + 150 worked practice problems (PDF). Study offline, ace the exam.
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Fast subnetting cheat sheet (free)
| CIDR | Subnet mask | Wildcard | Usable hosts | Block size |
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The magic-number method
Find the "interesting octet" (where the mask isn't 255 or 0). The block size = 256 − that mask octet. Subnets start at multiples of the block size; the network your IP belongs to is the largest multiple ≤ your IP's octet. Broadcast = next network − 1.
How to practice subnetting effectively
Subnetting is a timed skill: on the CCNA and Network+ you need answers in under 30 seconds without a calculator. Drill the mixed mode above daily until the block-size math is automatic. Then grab the printable Mastery Kit to practice offline and on paper the way the real exam works.