Which DNS record contains administrative information such as serial number and refresh rates for a zone?

• A. A record
• B. MX record
• C. CNAME record
• D. SOA record

Answer: (D)

In DNS, the Start of Authority (SOA) record holds the administrative and control information for a zone. It identifies the primary name server for the zone and the email of the zone administrator, and it tracks the zone’s version and timing parameters. The serial number is updated whenever the zone data changes, which signals secondary (slave) servers to fetch the updated zone. The refresh value tells secondaries how often to check with the primary for updates; the retry value specifies how long to wait before retrying after a failed refresh; the expire value defines how long secondaries should keep data if the primary becomes unreachable; and the minimum TTL sets the default caching duration for records in the zone (and is used for negative responses). Because these pieces are all about zone administration and synchronization, the SOA record is the one that contains this information. A records map names to IPv4 addresses, MX records designate mail servers, and CNAME records create aliases, but none carry the zone’s administrative data.