Glossary / SOA record

SOA record (start of authority)

An SOA record (start of authority) is the "passport" of a DNS zone: it sits at the top of the zone and holds its administrative data. It names the primary name server, the admin's email, the zone version (serial), and refresh timers. Every domain has exactly one SOA.

The serial is the zone's version number. Every time you edit records it should go up. Secondary DNS servers watch the serial and, if it is higher than theirs, pull a fresh copy of the zone. Forget to raise the serial and your changes never spread.

The SOA timers (refresh, retry, expire, minimum TTL) control how often secondaries check with the primary and how long answers are cached, including "no such record" answers. So SOA even affects how fast your changes propagate.

An ordinary site owner rarely edits SOA by hand - the DNS provider creates it. But when DNS behaves strangely, the serial and timers in the SOA help you tell whether the zone has updated.

Example

example.com.  3600  IN  SOA  ns1.tomishost.com. admin.example.com. 2026072101 7200 3600 1209600 3600

Common mistakes

• Editing records but not bumping the serial, leaving secondary servers on the old zone.
• Reading the admin email in SOA literally; the first dot stands for @, so admin.example.com means admin@example.com.
• Setting a very high minimum TTL, so "empty" answers cache for a long time and slow down fixes.
• Assuming you can have several SOA records; a zone is allowed exactly one.

Related terms

• A record A record (DNS address record)
• AAAA record AAAA record (DNS IPv6 record)
• CNAME record CNAME record (DNS alias)
• MX record MX record (mail exchanger)
• TXT record TXT record (DNS text record)