The SOA & Serial tool retrieves the Start of Authority record from every authoritative name server for a domain and compares the serial numbers to confirm that all servers are in sync after a zone edit.
Enter a domain name (example.org) and run the tool. The probe queries each authoritative name server for its SOA record and compares the serials.
Input: Domain — e.g. example.org.
The output lists each name server with its SOA serial, refresh, retry, expiry and minimum TTL. The summary reports whether all serials agree. Mismatched serials mean one or more secondaries have not yet transferred the latest zone — a common cause of inconsistent DNS answers across resolvers.
→ Confirm all authoritative servers are in sync after a zone edit.
→ Find a lagging secondary causing inconsistent DNS answers.
→ Verify SOA timing values match your operational requirements.
→ Diagnose a split-horizon or multi-provider DNS inconsistency.
It means one or more authoritative name servers are serving an older copy of the zone than the primary. Until they complete a zone transfer, resolvers hitting those servers get stale answers, causing inconsistent behaviour for different users.
It polls the primary every refresh interval and compares serials; if the primary’s serial is higher it initiates a transfer. For faster propagation, the primary can send a NOTIFY immediately after a change.
Refresh is how often the secondary checks the primary; retry is the interval after a failed check; expiry is how long the secondary will keep serving the zone if it cannot reach the primary before it stops answering entirely.