RFC 958 introduced network time protocol. Network time protocol can be utilised to synchronise a set of clocks on network devices on a client to server model.
Synchronising time is important on network devices. Time is used for many different features on network devices such as managing time specific passwords, key exchanges, checking the validity of a certificate, scheduled events such as specific timed access through a firewall. Time is also important for troubleshooting, such as reviewing system logs in aid of troubleshooting.
The client server model of NTP is based on a hierarchical model. At the top of the tree is an NTP server with an atomic clock. These servers are known as stratum 1 servers. An NTP device that queries a stratum 1 device is known as a stratum 2 device, and so on. The lower the stratum number the more likely the time is to be accurate.
NTP synchronisation is not quick, and usually requires at least a few polls to get accuracy within a couple of seconds. Gaining better accuracy requires even more polls over a longer duration of time.