Network Time Protocol Client Overview

An NTP client can be enabled when one or more NTP servers/peers is configured.

The NTP client maintains the server and peer state information as an association. The server and peer association is mobilized at startup, or after it has been configured. A statically configured server/peer association is not demobilized unless the configuration is removed/changed. A symmetric passive association is mobilized upon the arrival of an NTP packet from a peer which is not statically configured. This type of association is demobilized on error or timeout.

The NTP client operation can be summarized as follows:

The device is booted and the system initializes. The configured servers and peers are polled at the configured poll interval. Additional dynamically discovered servers/peers are also polled.
Multiple samples of server/peer times in the NTP packet are added to and maintained in the association database.
The selection, cluster, and combine algorithms choose the most accurate and reliable server/peer as system peer.
Note
Refer to RFC 5905.
The reference time from the system peer is used for system time synchronization.
The NTP client increases the poll interval from the minimum poll interval to the maximum poll interval value after the clock stabilizes.

After the system peer is chosen, the system time is synchronized using one of the following ways:

If the system time differs from the system peer by less than 128 milliseconds, then the system clock is adjusted slowly towards the system peer time reference time.
If the system time differs from the system peer by greater than 128 milliseconds, then the system clock is stepped to the system peer reference time. The old, time-related information stored in the server/peer association database is cleared.