[time-nuts] Recommendations for NTP server

Geoff Powell geoff at g8kbz.demon.co.uk
Sun Apr 23 17:49:24 EDT 2006

In article <92ECBF63-4331-4CF4-8AEE-B60824151EA1 at cs.cmu.edu>, David
Andersen <dga+ at cs.cmu.edu> writes
>You'll get more than you expect -- the offset you're observing on  
>ADSL is very likely wrong, because the delays your packets experience  
>on adsl aren't symmetric.  NTP assumes symmetry.  So I wouldn't  
>actually believe that a 1ms offset is really 1ms off, depending on  
>the RTT to your ISP.

Yes, I knew about that, but all I can go by as a newbie is what MRTG is
telling me - and it's telling me that my time offsets are too big...

>But there actually are ways to mitigate the offset spikes.  You might  
>be able, for instance, to configure your gateway to prioritize NTP  
>packets over everything else, which will help with half of the  
>problem.  You won't be able to do the same at your ISP, of course, so  
>it's not a perfect solution.

A Netgear DG814 is too brain-dead to understand QoS. One thing at a

>Installing a local GPS-synched server is the right answer if you  
>really care.  And it's fun. :)  The Soekris boxes rock.  I assume  
>you've already seen Poul-Henning Kamp's page about using his net4801  
>with FreeBSD to act as a high precision timeserver?  If you want sub- 
>microsecond, you'll probably have to replace the oscillator on the 4801.

Yes, I've read his page on that - as an electronic engineer, I even
understood it! That will be the next stage - I'll settle for units of
microseconds for the moment.

>And - most OSes should do the trick.  FreeBSD has a really nice  
>precision timekeeping interface, though -- and it makes a marvelously  
>solid time server.  I'm running it on a few Net4801s and recommend  
>it.  You can very easily build an image for it using another bit of  
>phk's magic called 'nanobsd' (it's in the source tree).

As I just asked John A. - is it in the default kernel?

Thanks for your comments,
Geoff Powell

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