Every term the site uses, in plain English, each linked to the chapter that explains it properly. Type in the box to filter; it searches the definitions too, so "cache" finds TTL and negative caching. Below the list: the limits, response codes and dates worth knowing by heart.
Common mix-up: a domain and a zone are not the same thing. The domain jelia.nyc is every name that ends in jelia.nyc. The zone jelia.nyc is only the part of that branch its own servers answer for; any sub-branch it has delegated to other servers is a separate zone.
Every DNS response carries a four-bit response code (RCODE) in its header; EDNS extends it. Chapter 14 shows how to read them in dig output.
| Code | Name | What it means |
|---|---|---|
| 0 | NOERROR | The query worked. With an empty answer section it means NODATA: the name exists, the type does not. |
| 1 | FORMERR | The server could not understand the query. |
| 2 | SERVFAIL | The server failed to get an answer, often an unreachable authority or a DNSSEC validation failure. |
| 3 | NXDOMAIN | The name does not exist, for any type. |
| 4 | NOTIMP | The server does not support this kind of query. |
| 5 | REFUSED | The server will not answer this client, by policy. |
The history chapter tells the stories behind them.
| Year | What happened |
|---|---|
| 1983 | Paul Mockapetris publishes RFC 882 and RFC 883, the first DNS specifications, replacing the single shared HOSTS.TXT file |
| 1987 | RFC 1034 and RFC 1035, the definitions of DNS still in force |
| 1998 | ICANN is founded to coordinate the root zone and top-level domains |
| 2005 | The current DNSSEC specifications, RFC 4033, 4034 and 4035 |
| 2008 | Dan Kaminsky's cache-poisoning disclosure (CERT VU#800113) leads resolvers to randomize source ports |
| 2010 | The root zone is signed with DNSSEC |
| 2016 · 2018 · 2022 | DNS over TLS (RFC 7858), DNS over HTTPS (RFC 8484), DNS over QUIC (RFC 9250) |