Networking from Scratch (lesson 5) — the difference between switches and routers in plain English, with the MAC table vs routing table side by side, a packet walked end-to-end through both, and why your home box is secretly two devices crammed into one chassis.
Networking from Scratch (lesson 4) — the DHCP DORA four-packet exchange, lease and renewal mechanics, common DHCP options, the cross-subnet relay agent, and the ARP request/reply that turns an IP into the MAC the wire actually delivers to. Plus the symptoms of common failure modes.
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.
Networking from Scratch (lesson 1) — an end-to-end walkthrough of the eight things that happen between clicking a link and seeing the page on your screen. DNS, ARP, routing, TCP, TLS, HTTP, render, and where to look when each one breaks. No prior experience required.
Working reference for the Linux file and directory commands you type thousands of times a year. ls with -l/-la/-lh/-ltr/-ld variations, the cd - bounce trick, mkdir -p for idempotent path creation, cp -a for archive-style copies (with the trailing-slash gotcha), mv for both rename and move, rm -rf danger and the safer find -print -> find -delete pattern, find by name/size/mtime/owner with -exec and -delete, locate vs find (locate is fast but stale), symbolic links with ln -s, the 10 commands that cover 95 percent of daily use, and the common pitfalls (rm -rf with unset variable, trailing-slash confusion, unquoted spaces in filenames).
