Subnetting Practice Set: 25 Problems with Full Solutions
Networking from Scratch (lesson 13) — twenty-five subnetting practice problems across five difficulty tiers (classful warm-up, /25-/30 in the 4th octet, octet-boundary, VLSM carving, real-world planning) with step-by-step solutions for every one. Designed to take you from "I read the math" to "subnetting is reflexive" in one sitting.