Which UDP port is used by the Network Time Protocol (NTP) for communication?

• A. Port 53
• B. Port 123
• C. Port 161
• D. Port 67

Answer: (B)

NTP uses UDP for lightweight, time-critical communication and standardizes on port 123 for all its traffic. This means clients send their time requests to a server listening on UDP port 123, and the server responds from its own UDP port 123 back to the client’s ephemeral port. Defining a single, well-known port makes handshakes and time exchange predictable across devices and networks, which is essential for accurate clock synchronization. RFC 5905 documents this usage, so you’ll frequently see NTP traffic on UDP 123 in real networks. By contrast, the other ports are tied to different protocols—port 53 is DNS, port 161 is SNMP, and port 67 is DHCP server—so they don’t apply to NTP.