Routers work with numbers, people with names. The Domain Name System bridges the two: it translates example.nl into the address the site sits at. It is a distributed database with no central copy — each domain publishes its own data.
The main record types
- A — the IPv4 address for a name
- AAAA — the IPv6 address for a name
- MX — where mail for this domain should go, with a priority
- NS — which nameservers are authoritative for this domain
- TXT — free text, in practice mostly SPF, DKIM and domain verifications
- CNAME — this name is an alias for another name
- SOA — the administrative details of the zone
- CAA — which certificate authorities may issue a certificate
TTL
Every answer carries a Time To Live: how many seconds a resolver may remember it before asking again. A low TTL makes a change visible quickly, a high TTL saves traffic. Anyone planning a migration lowers the TTL a day in advance.