What does DNS primarily use to serve requests?

• A. TCP on port 80.
• B. The User Datagram Protocol (UDP) on port number 53.
• C. ICMP.
• D. HTTP on port 443.

Answer: (B)

DNS is built around small, fast request/response exchanges. For ordinary name-resolution queries, a client sends a compact request as a UDP datagram to port 53 on the DNS server. UDP is chosen because it has minimal overhead and provides low-latency delivery, which is ideal for frequent, tiny lookups. If a response would not fit in a single UDP packet or a reliable delivery is needed (for example, for larger transfers like zone transfers or DNSSEC-related data), the conversation can fall back to TCP on port 53. Other protocols like ICMP or HTTP on different ports aren’t used to serve standard DNS lookups, reinforcing that UDP on port 53 is the primary mechanism.