Subnetting Basics: CIDR and VLSM

A practical, ground-up guide to IPv4 addressing, subnet math, CIDR notation, and Variable-Length Subnet Masking for network engineers and certification candidates.

Textbook

Read the full textbook Long-form companion to the chapter guides →

Chapter Guides

  1. 1 Why Subnetting Exists: The Big Picture
  2. 2 IPv4 Addressing and Binary Fundamentals
  3. 3 Classful Addressing and Its Limits
  4. 4 Subnet Masks Explained
  5. 5 CIDR Notation and Prefix Length
  6. 6 Anatomy of a Subnet: Network, Hosts, and Broadcast
  7. 7 Subnetting Step by Step: Fixed-Length Subnetting
  8. 8 VLSM: Variable-Length Subnet Masking
  9. 9 Route Summarization and Supernetting
  10. 10 Practical Design, Tools, and Troubleshooting
  11. 11 Mastery, IPv6 Preview, and Next Steps