Configuring an NTP primary clock

If both manners are configured, the device selects an optimal clock source by comparing the clocks determined in the two manners. The clock of a lower stratum is preferred.

An authoritative clock is used as a reference time source for a synchronization subnet, and is located at the top of a hierarchical structure on the synchronization subnet. The authoritative clock is stratum0. The current authoritative clock is mostly a Radio Clock or the Global Positioning System. The time of the authoritative clock is synchronized through the broadcast UTC time code other than NTP.

In actual circumstances, the NTP server synchronized with the authoritative clock is set as stratum1, and is used as a master reference clock source. Other devices on the network synchronize their clocks with the clock of the NTP server, which means the local clock of the NTP server is configured as the NTP primary clock. The NTP distance from a device on the network to the master reference clock source, that is, the number of NTP servers on the NTP synchronization chain, determines the stratum of the clock on the device.

As shown in Figure 3-1, SwitchA is the primary clock, and the clock stratum is 1. The clock synchronization direction is from SwitchA to SwitchB, and further to SwitchC. Only after the SwitchB is synchronized with SwitchA, SwitchC can synchronize its clock with the clock of SwitchB. After all the devices on the synchronization subnet are synchronized, SwitchB and SwitchC are respectively stratum2 and stratum3.

Figure 3-1  NTP synchronization subnet

After the local clock is configured as the reference clock, the local device can be used as the clock source to synchronize other devices on the network. Confirm before this configuration, so as avoid clock errors on the network.