Stratum
stratum
Stratum is the designation for each level in NTP's hierarchical model, ranging from Stratum 0 (atomic clocks and GPS receivers) to Stratum 15, indicating distance from the reference time source.
NTP (Network Time Protocol)
ntp
Overview
The Network Time Protocol (NTP) is one of the oldest Internet protocols still in active use, dating back to 1985. It synchronizes the clocks of computers to a reference time source with accuracy typically within a few milliseconds over the public Internet, and sub-millisecond accuracy on local area networks.
Stratum Hierarchy
NTP uses a hierarchical system of time sources called strata. Stratum 0 devices are high-precision timekeeping instruments such as atomic clocks or GPS receivers. Stratum 1 servers are directly connected to Stratum 0 devices. Each subsequent stratum synchronizes from the level above, with Stratum 15 being the maximum. Stratum 16 indicates an unsynchronized device.
Security Considerations
NTP traffic is often unencrypted and unauthenticated, making it vulnerable to man-in-the-middle attacks that could shift a system's clock. NTS (Network Time Security), standardized in RFC 8915, adds authentication and encryption to NTP. Cloud providers like AWS offer their own time synchronization services (Amazon Time Sync Service) that provide authenticated, low-latency time sources.
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