Glossary
DNS RECORDS

DNS Zone

A portion of the DNS namespace administered by a single authority. Delimited by NS records and controlled by a single SOA record.

DNS Zone is a contiguous portion of the DNS namespace under a single administrative authority. Zones are delimited by NS records at their boundaries and controlled by exactly one SOA record at their apex.

Zone vs Domain

The terms are not synonymous:

  • Domain — a name in DNS (e.g., example.com)
  • Zone — the set of records administered together as one file

example.com might be one zone containing all *.example.com records. Or blog.example.com might be delegated to a separate zone hosted on a different nameserver — that delegation is a zone cut.

Zone Cut

An NS record inside a parent zone that points to different nameservers is a zone cut. The child zone becomes its own administrative unit with its own SOA.

example.com.        NS   ns1.example.com.
blog.example.com.   NS   ns.blog-host.com.   ← zone cut

Master vs Slave

  • Master (primary) — the authoritative source, defined by the SOA’s mname field
  • Slave (secondary) — pulls the zone via AXFR/IXFR from the master, serves the same data

Secondaries provide redundancy but never accept updates directly.

Zone Files

Historically zones were flat text files (BIND format). Modern DNS services (Route 53, Cloudflare, NS1) store zones as records in a database and generate DNS responses on the fly.

Read what an SOA record is, check the nameserver glossary entry, and the NS record entry.

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