DNS SOA Records

DNS Start of Authority (SOA) records are records describing important information about the DNS zone such as the contact information, the serial number showing when it was last updated, how long before a zone expires, etc.

E.g.
Here we can see the SOA record for redcross.org:

% dig redcross.org soa +short
arcdns1.redcross.org. netops.redcross.org. 2021040612 14400 7200 1209600 3600
%
Here we can see:

• arcdns1.redcross.org. is the primary master nameserver for the zone
• netops@redcross.org. (SOA records don't specify the @ symbol) is the primary contact for the zone
• 2021040612 is the serial number of the zone
• 14400 is the refresh value, the value used by secondary nameservers to refresh their copy of the zone
• 7200 is the retry value, the number of seconds a secondary should wait before retrying an unreachable master
• 1209600 is when the zone data expires and a secondary server should stop serving the stale data
• 3600 is the number of seconds negative responses should be cached