example.com. 3600 IN SOA ns.icann.org. noc.dns.icann.org. 2024081401 7200 3600 1209600 3600
Every DNS zone has exactly one SOA record (start of authority) at its apex. It doesn’t direct traffic; it describes the zone.
Fields, in order
- MNAME — the primary name server.
- RNAME — the administrator’s email, with the first dot standing for @ (
hostmaster.example.com= [email protected]). - Serial — a version number secondary servers compare to decide whether to transfer the zone. A common convention is
YYYYMMDDnn. - Refresh, Retry, Expire — how often secondaries check for updates, how soon they retry, and when they stop answering if the primary is unreachable.
- Minimum — today used as the TTL for negative answers (NXDOMAIN) per RFC 2308.
Frequently asked questions
- Why didn't my DNS change reach secondary servers?
- Usually because the SOA serial wasn't increased. Secondaries only transfer the zone when the serial goes up.
- What does the SOA minimum value do?
- It sets how long resolvers cache 'this name does not exist' answers.