Inspect a domain's Start of Authority record: primary nameserver, serial, and refresh timers.
Enter a domain to look up its SOA records.
The SOA (Start of Authority) record holds administrative metadata for a DNS zone: the primary nameserver, the zone administrator's email, a serial number that increments on every change, and the timers that govern how secondary servers refresh.
Checking the serial number is a quick way to confirm a zone change has been published. This tool shows every SOA field for a domain.
The serial increments each time the zone changes. Secondary nameservers compare it against their cached copy to decide whether to pull an update. If the serial did not change, your edit has not been published yet.
They control secondary nameserver behaviour: refresh is how often to check for updates, retry is how long to wait after a failed check, and expire is how long a secondary keeps serving data if it cannot reach the primary.
Yes. A valid DNS zone must have exactly one SOA record at its apex. It is created automatically when you set up a zone with your DNS provider.
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