Which DNS record defines the primary name server for the domain and the duration of DNS caching?

• A. It maps a domain name to an IP address.
• B. It defines the mail exchange server for the domain.
• C. It specifies the authoritative zone transfer policy.
• D. It defines the primary name server for the domain and the duration of DNS caching.

Answer: (D)

In DNS, a resource record has a time-to-live (TTL) that tells resolvers how long to cache the information, and the NS (name server) record identifies which servers are authoritative for the domain. The option describing both the primary name server and the caching duration matches exactly with how NS records work: they designate the domain’s authoritative servers and carry a TTL that controls how long that information is cached by DNS resolvers.

The other choices describe different DNS records or concepts: mapping a domain to an IP address is an A (or AAAA for IPv6) record, which is not about the authority or caching duration; defining the mail exchange server is an MX record; and a zone transfer policy is not defined by a DNS resource record at all but by server configuration.