NTP architecture
NTP uses stratums 1 to 16 to define clock accuracy, as shown in Figure 33. A lower stratum value represents higher accuracy. Clocks at stratums 1 through 15 are in synchronized state, and clocks at stratum 16 are not synchronized.
Figure 33: NTP architecture
A stratum 1 NTP server gets its time from an authoritative time source, such as an atomic clock. It provides time for other devices as the primary NTP server. A stratum 2 time server receives its time from a stratum 1 time server, and so on.
To ensure time accuracy and availability, you can specify multiple NTP servers for a device. The device selects an optimal NTP server as the clock source based on parameters such as stratum. The clock that the device selects is called the reference source. For more information about clock selection, see the related protocols and standards.
If the devices in a network cannot synchronize to an authoritative time source, you can perform the following tasks:
Select a device that has a relatively accurate clock from the network.
Use the local clock of the device as the reference clock to synchronize other devices in the network.