Port 123

Q: What is port 123?

Network time synchronization (NTP) NTP (Network Time Protocol) on UDP port 123 synchronizes computer clocks to millisecond accuracy. Every server, router, PC, and mobile device relies on NTP. Accurate time is critical for TLS certificate validation, Kerberos authentication, log correlation, and distributed systems. A publicly accessible NTP server can be abused for NTP amplification DDoS attacks (up to 556x amplification). Common public NTP servers include pool.ntp.org and time.cloudflare.com.

NTP

Network time synchronization (NTP)

Port

123

Protocol

UDP

Service

NTP

Security

Restricted

Full name: Network Time Protocol

What is port 123?

NTP (Network Time Protocol) on UDP port 123 synchronizes computer clocks to millisecond accuracy. Every server, router, PC, and mobile device relies on NTP. Accurate time is critical for TLS certificate validation, Kerberos authentication, log correlation, and distributed systems. A publicly accessible NTP server can be abused for NTP amplification DDoS attacks (up to 556x amplification). Common public NTP servers include pool.ntp.org and time.cloudflare.com.

Related ports

← All ports