What is a network time protocol (NTP)?
Answer
NTP (Network Time Protocol) synchronizes clocks across network devices to a reference time source. Accurate time is critical for: log correlation (correlating events across devices, security forensics), certificate validation (TLS certificates have validity periods), authentication protocols (Kerberos requires clocks within 5 minutes), distributed databases, and financial transactions. NTP uses a hierarchical structure of time sources called strata: Stratum 0 — highly accurate reference clocks (GPS, atomic clocks). Stratum 1 — servers directly connected to Stratum 0 sources. Stratum 2 — servers synchronized to Stratum 1, and so on. NTP uses UDP port 123. PTP (Precision Time Protocol, IEEE 1588) achieves sub-microsecond accuracy for financial trading and telecom. SNTP is a simplified NTP for devices that do not need full NTP precision. Configure NTP on all network devices — clock skew causes hard-to-diagnose problems. Use at least two NTP sources for redundancy. NTPsec and Chrony are modern replacements for the legacy ntpd daemon.