Working notes on DNS, propagation, and running the monitor. Short, practical, command-line first. The Learn DNS series builds the system up from the ground, one numbered piece at a time.
Names in, numbers out, for the whole internet, with no central list. What DNS replaced, the three ideas that make it work (hierarchy, delegation, caching), and why caching is also the reason a change is never instant.
One name, taken apart label by label: the root dot, the top-level domain, the registrable
domain (apex), and subdomains. Label rules, the public-suffix problem
(co.uk, github.io), and how a zone differs from a domain.
One query from your keyboard to the authoritative answer: stub resolver, recursive
resolver, root, TLD, authoritative, and the cache at every hop. With an annotated
dig +trace and what each cached hop means for propagation.
Three organisations sit behind every domain, and only one of them is ever the reason
a nameserver change feels slow. The registry / registrar / registrant split, what the
registry actually stores, and how to see each part with dig and
whois.
Which commands actually tell you when a nameserver change has taken - and why "propagation" is two changes, not one. A copy-paste sequence for a Namecheap to Cloudflare move, from the registry push to the SSL check.