Recipe 14.8 Changing NTP Synchronization Periods

14.8.1 Problem

You want to adjust how often routers send NTP packets to verify clock synchronization.

14.8.2 Solution

You cannot manually change NTP's polling rates. The protocol has an adaptive algorithm that automatically adjusts the polling interval.

14.8.3 Discussion

NTP is an extremely efficient protocol that actively monitors all aspects of network timing to adjust its configuration accordingly. Upon initialization of NTP, a router sets its cycle to poll about once every 64 seconds. As the local clock becomes synchronized and stable, the router will adaptively back off the poll cycle to a maximum of 1024 seconds (roughly 17 minutes):

Router>show ntp associations
   
      address         ref clock     st  when  poll reach  delay  offset    disp
*~172.25.1.1       130.207.244.240   2   440  1024  377     1.6   -3.23     5.6
+~172.25.1.3       204.152.184.72    2   829  1024  377     1.7    8.06     0.9
* master (synced), # master (unsynced), + selected, - candidate, ~ configured
Router>

Note that the poll cycle for the two configured servers has been throttled back to 1024 seconds. This indicates that the router is in a stable network and the time services are consistently accurate. This also illustrates the remarkable efficiency of NTP.