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Network Time Protocol (NTP) is a timing protocol that allows time synchronization across devices on a network to the Coordinated Universal Time UTC time. NTP operates on UDP port 123.
NTP has no awareness of time zone TZ or day light savings time DST.
Services such as authentication, synchronization, and directory services are all time sensitive and require time synchronization to operate properly.
NTP uses a hierarchical system of time sources called Stratum.
The are 16 valid levels of Stratum starting at 0 and ending with 15. Stratum 16 is invalid and means device not synchronized.
Stratum 0 is the actual atomic, GPS, or radio clock - The Clock
Stratum 1 is a computer directly attached to a Stratum 0 device. - Directly attached to clock
Stratum 2 is a networked computer synchronizing with at Stratum 1 computer. - Syncs via network
Stratum 3 is serviced via network by Stratum 2 and so on. - Syncs via network
A NTP client will regularly poll multiple servers to determine is time.
The current of NTP is Version 4. For technical specifications review the RFC’s below.
NTPv4 is backward compatible to version 3:
RFC’s Relating to NTPv4:
