Which protocol uses UDP port 123 for clock synchronization in networks?

• A. Simple Mail Transfer Protocol (SMTP)
• B. Network Time Protocol (NTP)
• C. Domain Name System (DNS)
• D. Hypertext Transfer Protocol (HTTP)

Answer: (B)

Clock synchronization across devices uses a protocol designed to share time data efficiently. Network Time Protocol communicates time information over UDP port 123, allowing frequent, low-overhead exchanges between clients and servers. Using UDP keeps the messages lightweight and fast, which is important for time updates where a minor loss is acceptable and retries are quick. NTP works by exchanging timestamps to determine the local clock offset and adjust timing to keep devices in sync across the network. Other common services—email, DNS, and web traffic—serve different purposes and run on their respective ports, not for clock synchronization. So, the protocol that uses UDP port 123 for clock synchronization is Network Time Protocol.