What Is NTP?
The Network Time Protocol (NTP) is an application layer protocol in the TCP/IP protocol suite. It is used to synchronize the clock between the client and the server to provide high-precision time correction. The NTP server receives accurate Coordinated Universal Time (UTC) from an authoritative clock source, such as an atomic clock or GPS. Then, the NTP client requests and receives time from the NTP server.
NTP relies on User Datagram Protocol (UDP) port 123.
NTP Stratum
NTP allows a server to receive accurate UTC time from an authoritative clock source (such as an atomic clock or GPS) and a client to request and receive time from a server.
NTP uses a hierarchical structure of time sources. Each level of this hierarchy is termed a stratum. Generally, an NTP server synchronized to an authoritative clock runs at stratum 1. This NTP server functions as the primary time server to provide clock synchronization for other devices on the network. Stratum 2 servers obtain time from stratum 1 servers, stratum 3 servers obtain time from stratum 2 servers, and so on. The clock stratum ranges from 1 to 16. A smaller value indicates a higher precision. The clocks at stratums 1 to 15 are synchronized. The clocks at stratum 16 are not synchronized and cannot be used.
For more information, see What Is NTP?
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