Port 123: NTP
Port 123 is NTP, which keeps clocks in sync across a network. Accurate time matters for logs, certificates, and Kerberos, so NTP is a quiet but critical service.
UDPCore servicesUnencrypted by defaultIANA assigned
| Port number | 123 |
|---|---|
| Service | Network Time Protocol |
| Protocol | UDP |
| Category | Core services |
| Default encryption | No |
Security note. Port 123 is not encrypted by default. Restrict it to trusted networks, or use an encrypted alternative where one exists, to avoid exposing credentials and data in transit.
Frequently asked questions
What is port 123 used for?
Port 123 is NTP, which keeps clocks in sync across a network. Accurate time matters for logs, certificates, and Kerberos, so NTP is a quiet but critical service.
Is port 123 TCP or UDP?
Port 123 (NTP) uses UDP.
Is port 123 secure?
Port 123 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 123 on my firewall?
Only if you specifically need NTP. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.