Port
Port 123 — NTP
Port 123 (UDP) is used by NTP. Network Time Protocol — synchronises clocks across devices.
Port 123 at a glance
| Property | Value |
|---|---|
| Port number | 123 |
| Transport | UDP |
| Service | NTP |
| Category | Well-known port |
What it is used for
Network Time Protocol — synchronises clocks across devices.
Security considerations
Used in amplification DDoS. Disable monlist; authenticate NTP where possible.
See our full TCP/UDP port reference and learn how firewalls filter ports in the CyberOps course.
Frequently asked questions
What is port 123 used for?
Port 123 (UDP) is used by NTP. Network Time Protocol — synchronises clocks across devices.
Is port 123 TCP or UDP?
Port 123 uses UDP.
Is it safe to open port 123?
Used in amplification DDoS. Disable monlist; authenticate NTP where possible.
Related
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