Recipe 14.15 Setting the Clock Period

14.15.1 Problem

You want to improve on the default value in the ntp clock-period xxxxxx command that automatically appears when you configure NTP on your router.

14.15.2 Solution

The router will automatically generate an ntp clock-period line that it uses to help speed resynchronization after a reboot. Leave it alone:

Router#show running-config | include clock-period
ntp clock-period 17180200
Router#

Do not attempt to remove or modify the ntp clock-period command. The router automatically generates this command to compensate for internal timer inaccuracies.

14.15.3 Discussion

Do not modify or remove this statement from the router configuration. The router automatically adds this statement to the configuration when you enable NTP. After initializing NTP, the router tunes the clock period to compensate for precision problems with the router's internal clock.

The router will actually change the NTP clock period as it improves its estimation of how fast or slow its clock runs. For this reason, Cisco suggests that all routers have their configurations saved to NVRAM one week after enabling NTP. This ensures that the saved clock period is accurate for the next router initialization and allows for quicker NTP synchronization.