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Port 123 (NTP) — What It Is and How to Use It

Port 123 is the standard port for the Network Time Protocol (NTP). NTP is a networking protocol used for clock synchronization between computer systems over packet-switched, variable-latency data networks, ensuring accurate timekeeping across devices.

Last updated: 2026-06-11

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Port Number 123
Protocol NTP

Common Use Cases

  • Synchronizing clocks on servers and workstations
  • Maintaining accurate timestamps for logs and security events
  • Coordinating distributed systems and applications

Interactive Command Builder

nc -zv example.com 123

Check if Port 123 is Open

sudo netstat -tulnp | grep :123
Get-NetTCPConnection | Where-Object {$_.LocalPort -eq 123}
⚠️ Security Note: NTP servers can be vulnerable to attacks if not properly configured and patched. Monitoring and restricting access to NTP servers is crucial to prevent time manipulation and denial-of-service attacks.

Related Ports

Port 53 Port 80 Port 443

Frequently Asked Questions

Is port 123 dangerous to leave open?

Leaving port 123 open is necessary for NTP to function, but it can be a security risk if the NTP server is not properly configured and maintained. Vulnerable NTP servers can be exploited for amplification attacks or to manipulate time, leading to various security issues. Regularly update your NTP software and restrict access where possible.

What service uses port 123?

The Network Time Protocol (NTP) service uses port 123 for both UDP and TCP, although UDP is the more commonly used transport protocol.