Recursive DNS lookup is best described as:

• A. Querying only the local DNS cache
• B. Querying multiple DNS servers on behalf of the client to resolve the name
• C. Returning an error if the domain does not exist
• D. Querying the root servers and recursively walking the DNS hierarchy on the client’s behalf

Answer: (D)

Recursive DNS lookup means the resolver handles the entire process of resolving a domain name on behalf of the client. It starts at the root DNS servers, then follows referrals down the hierarchy to the appropriate top-level domain servers and eventually to the domain’s authoritative servers, repeating queries until it gets the final resource record or an NXDOMAIN, and then returns that result to the client. This is what makes the resolver act “on behalf of” the client, performing all the steps instead of the client having to chase each referral itself.

Using only the local cache would bypass live resolution, and wouldn’t describe the full, on-demand lookup. An iterative approach would involve the client (or a server) following referrals step by step rather than having the resolver perform the complete walk. Simply returning an error doesn’t capture the resolving process itself.