What Is a DNS SOA Record?

What the SOA Record Contains

Every DNS zone has exactly one SOA (Start of Authority) record. It defines authoritative metadata about the zone:

example.com.  3600  IN  SOA  ns1.example.com.  hostmaster.example.com. (
              2026010101  ; Serial
              3600        ; Refresh
              900         ; Retry
              604800      ; Expire
              300 )       ; Minimum TTL

Fields Explained

• Primary nameserver: the authoritative master nameserver for the zone
• Responsible party: the zone administrator's email (the first dot replaces @)
• Serial: a version number, incremented on every zone change. Secondary nameservers compare serials to detect updates.
• Refresh: how often secondary nameservers check for updates (seconds)
• Retry: how long a secondary waits before retrying a failed refresh
• Expire: how long a secondary serves stale data if the primary is unreachable
• Minimum TTL: the default TTL for negative responses (NXDOMAIN caching)

Why the Serial Matters

When you update DNS records, you must increment the SOA serial. Secondary nameservers poll the primary using the refresh interval and compare serials. If the primary's serial is higher, they perform a zone transfer to get the updated records.

The conventional format is YYYYMMDDNN (date + two-digit revision number): 2026010101 means the first revision on 2026-01-01.

Inspect SOA records with our DNS Lookup tool.