What is NTP


Many applications are using time as a most important input for correctly working service. According to this NTP (Net Time Protocol) was invented. It is providing time synchronization between NTP Server and NTP Client with using of standard network infrastructure.

What is provided at NTP protocol

NTP is widely used for time synchronization between devices connected to network. For correct working NTP service is important to have source of reference clock (Stratum 0 NTP server) such as a radio, satellite receiver or telephone modem. Typically accuracy of NTP service is less than a millisecond on LANs and up to a few milliseconds on WANs. Typical NTP configurations is using multiple redundant servers and diverse network paths to achieve high accuracy and reliability of the service.

NTP Stratum definition

Definition of Stratum level related to NTP service is equivalent to distance from the reference clock. NTP protocol is supporting 0-15 Stratum level’s. Stratum 16 Level is used for unsynchronized status.

Stratum 0

Stratum 0 server are known as well as reference clock. In this case we are speaking about high precision timekeeping device. Usually an used atomic clock, GPS clock or special device connected to a NTP server.

Stratum 1

Stratum 1 servers is synchronizing his local server time with Stratum 0 servers.

An example of Stratum 1 is a server with GPS receiver. In this NTP stratum/level it is possible to interconnect more Stratum 1 servers between each other, this will provide us failover solution in the case that one of the Stratum 0 server will be not reachable.

Stratum 2

Stratum 2 servers are synchronizing they local server time with Stratum 1 servers.

At this NTP stratum/level it is possible to use more as one Stratum 1 server for time synchronization, but as well it is possible to use another Stratum 2 server for time synchronization. Stratum 2 NTP servers can be used as time source for larger list of servers servers (typically for a DC)

Stratum 3

Stratum 3 servers are synchronizing they local server time with Stratum 2 servers.

In most scenarios at this level we are already speaking about NTP clients that are using Stratum 2 as time source and not providing the NTP service to any NTP client. Any way in some cases at this level it is still possible to deploy as well standard NTP server that will provide the service to several NTP Clients. At this point it is important to understand that at each Stratum level we are getting higher inconsistency to reference time.


NTP protocol is supporting 0-15 Stratum levels. Stratum 16 Level is used as unsynchronized status.


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