Which protocol uses UDP port 123?

The correct answer is the Network Time Protocol (NTP), which operates over UDP port 123. NTP is a protocol used to synchronize the clocks of computers over a network. Accurate timekeeping is essential for various applications, including logging events, coordinating tasks, and ensuring secure communications. By using UDP (User Datagram Protocol), NTP can provide time synchronization with low latency and minimal overhead, as it doesn't require the reliable delivery mechanisms of TCP (Transmission Control Protocol).

In contrast, the other protocols mentioned serve different functions: HTTP is used for web traffic over port 80 and is based on TCP, DHCP facilitates dynamic IP address assignment typically over UDP ports 67 and 68, and DNS resolves domain names around UDP port 53. Each of these protocols has its specific use cases and transport protocols, distinguishing them from the time synchronization functions of NTP.