Which port is used by NTP?

The Network Time Protocol (NTP) is designed to synchronize the clocks of computers over a network. It specifically operates using a User Datagram Protocol (UDP) port for efficient time synchronization. The designated port for NTP is UDP port 123. This choice is correct because NTP needs a quick, efficient means of exchanging time-stamped messages between devices, and UDP is suitable due to its low-overhead nature.

In contrast, other ports listed in the choices serve different functions. For example, UDP port 161 is used for the Simple Network Management Protocol (SNMP), which is aimed at managing devices on IP networks. TCP port 67 is associated with the Dynamic Host Configuration Protocol (DHCP) for allocating IP addresses to clients on a network, while TCP port 123 does not have a specific use related to NTP, as NTP does not operate over TCP. Therefore, the correct understanding of NTP's operational protocol and port usage reinforces the reason why UDP port 123 is the appropriate choice for this question.