Recap: DNS

A tree of servers, a record per kind of answer, and a TTL that decides when a change is seen.

DNS turns names into addresses through a hierarchy of servers and a great deal of caching.

Resolution goes from a stub resolver to a recursive resolver, which asks a root server, a top-level domain server and the authoritative server in turn.
Records each hold one kind of answer: A and AAAA addresses, CNAME aliases, MX mail servers, TXT text and NS delegations.
A CNAME must stand alone at its name, so it cannot sit at a domain's root.
The TTL sets how long any cache may keep an answer; a change takes up to one TTL to reach everyone.
Transport: UDP on port 53, TCP for truncated answers and zone transfers, and DoH or DoT for privacy.
dig shows the answer, its remaining TTL and the server that gave it.

The resolution path, with the caches marked

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