How to use this guide

• Beginner (Parts I–IV): mental models, the 4-layer stack, addressing, and what actually happens when you load a web page.
• Intermediate (Parts V–IX): IP addressing math, routing, DNS, DHCP, NAT, and the full life of a TCP connection.
• Advanced (Parts X–XIV): congestion control algorithms, TCP tuning, TLS/QUIC, packet capture, and performance forensics.
• Expert (Parts XV–XVIII): kernel offloads, data-center and cloud networking, security attacks and defenses, and structured troubleshooting playbooks.

Each chapter ends with "Try it yourself" commands (Linux/macOS) and a "War story" — a realistic failure and its root cause.