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New Member

NTP clock-period

I have setup NTP on our 7200 router.

It is setup as NTP Master.

The system clock gets its time from the system calender. I have the command "clock calender-valid" so it is supposed to be authoritative.

My question is that the system clock very quickly diverges from the time on the system calender. I read somewhere that IOS is supposed to compensate by putting in the "ntp clock-period" command entry to allow the times to synch.

Is this the case? Does it do it by magic?

Has anyone else seen the system clock and system calender diverge??

Thanks for the help!

New Member

Re: NTP clock-period

Someone please correct me if I'm wrong, but I seem to remember that "clock calendar-valid" will read the calendar and set the system clock at startup. I don't believe that it is an ongoing function.

NTP MASTER will allow your router to function as an NTP time source. The one shouldn't directly affect the other.

That said, if you've configured NTP to also get time from an NTP server with a lower stratum, your clocks may diverge. Also, its possible that your system clock drifts too much... may be a job for TAC.


New Member

Re: NTP clock-period

Fair enough. "clock calender-valid" is a once off at startup, but then i would have hoped that the clock and calender would remain consistant.

What i see as a possible solution was this "ntp clock-period" command that is supposed to correct this.

Cisco Quote "The ntp clock-period command is added automatically to jump-start the NTP frequency compensation when the box is rebooted. (Do not configure this command manually.) This is essentially a representation of the frequency of the crystal used as the local timebase, and may take several days to calculate otherwise. Do a write mem after a week or so to save a good value. "

Any other comments?


New Member

Re: NTP clock-period

The ntp clock-period contains the actual frequency of the clock. This value is nudged up and down by NTP to keep the clock in synch. By saving the value obtained after a while, the clock starts out running at the correct speed at subsequent boots. There is normally no need to manually configure this value. However, I've seen cases where a bug set the period to value outside what NTP can correct. In this case, the clock will never synch up. Erasing the value and booting caused the processor to start the clock with default values, and allowed NTP to synch it.

New Member

Re: NTP clock-period

Don't you need NTP UPDATE-CALENDAR to keep the calendar in synch after boot.