Port 123 — NTP

UDP · Port 123/UDP is used for the Network Time Protocol (NTP), which enables devices to synchronize their clocks with a reference time source. This protocol is critical for maintaining accurate timestamps and ensuring the integrity of network transactions. Security relevance lies in preventing NTP amplification attacks, which can be used to launch DDoS attacks.

Port Number: 123
Service Name: NTP
Protocol: UDP
Common Software: ntpd, chronyd

Security Notes

Review IANA registry for port 123 usage. Apply principle of least privilege - only open ports that are required.

FAQ

What is port 123 used for?

Port 123 is used for NTP. Port 123/UDP is used for the Network Time Protocol (NTP), which enables devices to synchronize their clocks with a reference time source. This protocol is critical for maintaining accurate timestamps and ensuring the integrity of network transactions. Security relevance lies in preventing NTP amplification attacks, which can be used to launch DDoS attacks. Common software: ntpd, chronyd.

Is port 123 dangerous to leave open?

Review IANA registry for port 123 usage. Apply principle of least privilege - only open ports that are required.

How do I check if port 123 is open?

Use nmap: nmap -p 123 <target> or check locally: ss -tlnp | rg 123