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.
Networking from Scratch (lesson 3) — the four-line magic-number method for finding the network ID, broadcast, usable range, and next subnet for any /N. Three worked examples (including the awkward one across an octet boundary), a size cheat sheet, and five practice problems with answers.
Networking from Scratch (lesson 2) — what an IPv4 address actually is, why it has four numbers, what a subnet mask does, what CIDR notation means, and how a computer uses it to decide whether to deliver locally or send to the gateway. Plus the special address ranges every admin should recognise on sight.
