模块课程（4/4）
Ricorsione e iterazione
Recursion and iteration
In a recursive request, the client asks a resolver to return a final answer or an error. The resolver does the work. In iterative resolution, a server can reply with a referral: “I do not have that record, but ask this next server.”
A simple analogy
You ask a librarian to find a book. The librarian checks a catalogue, asks another library where needed, and comes back with the answer: that is recursion from your point of view. The libraries pointing one another onward behave iteratively.
An authoritative server usually does not recursively search the whole DNS tree for a client. It answers for its zone or provides a referral. A recursive resolver combines those iterative steps on the client’s behalf.
Check your understanding
Choose the best answer. This quiz runs locally and sends no DNS queries to real domains.
What does a recursive resolver promise its client?