What is the purpose of the SOA record in DNS?

• A. To store the domain's MX records for mail routing.
• B. To specify cache TTL values for zone data.
• C. To provide information about the domain's DNS zone and its authoritative server.
• D. To authorize zone transfers between primary and secondary servers.

Answer: (C)

The Start of Authority record identifies who is authoritative for a DNS zone and carries the essential metadata that governs how that zone is managed. It names the primary master server for the zone and the contact for the zone administrator, and it includes a serial number that increments whenever the zone data changes. It also sets timing parameters—how often secondary servers should check for updates (refresh), what to do if a refresh fails (retry), how long the data is considered valid if the master becomes unavailable (expire), and the minimum TTL used for negative responses. Together, these pieces tell resolvers and secondary servers where to get the official data and how to keep their copies in sync with the master.

This isn’t about storing mail routing information, which is the role of MX records. It isn’t a single global setting for cache TTLs; TTLs are defined per record and, historically, the minimum value in the SOA influenced negative caching, though its exact usage has evolved. It’s also not about authorizing transfers in isolation; the SOA provides the data that enables controlled transfers between the primary and secondary servers, but the records themselves and the transfer mechanism are separate. The key purpose is to define the zone’s authority and how that authoritative data should be propagated and validated.