Prefix length, the magic number, VLSM, and IPv6.
Master the math that decides where one network ends and the next begins. After this module you can subnet a /24 in your head, design an address plan with VLSM, and read an IPv6 address without flinching.
Welcome to module 2. Prefix length, the magic number, VLSM, and IPv6. I'll meet you again at the top of every chapter — this module's course coverage is Foundational, so don't rush it. Pick chapter 2.1 below to start.
Anyone can browse the syllabus and preview every chapter. Modules 2–8 come with the Course & Lab Pass and All-Access Max. A free account opens Module 1: Network Foundations end-to-end and saves your labs — start there, no card required.
An IPv4 address is 32 bits split into a network portion and a host portion. This chapter explains classful history (A/B/C), CIDR notation, and how every dotted-decimal address really lives in binary.
Memorize the prefix-to-mask table and you have memorized half of subnetting. This chapter gives you the table, the trick to derive any mask from scratch, and the formulas for hosts-per-subnet and subnets-per-supernet.
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A repeatable five-step recipe that gives you the network address, broadcast address, usable range, and number of hosts for any IPv4 address and mask in under 30 seconds. Worked examples included.