SOA record
An SOA (Start of Authority) record is the first record in every DNS zone, naming the zone's primary authoritative nameserver and administrator contact, plus a set of timing values -- serial number, refresh, retry, expire, and minimum/negative-cache TTL -- that control how secondary nameservers replicate the zone and how long a negative answer (a domain or record that doesn't exist) can be cached. The serial number is incremented on every zone change so secondaries know to pull an update; a serial that doesn't increase after an edit is a common, easy-to-miss cause of changes that silently fail to replicate to secondary nameservers. Unlike most record types, there is exactly one SOA record per zone, and it's typically surfaced alongside a domain's other records rather than looked up on its own, since it describes the zone itself rather than resolving to an address.
By AdminKit team, Netbase JSC · Updated