[ntp:questions] high precision tracking: trying to understand sudden jumps

Richard B. Gilbert rgilbert88 at comcast.net
Mon Mar 31 19:16:14 UTC 2008

David Woolley wrote:
> Heiko Gerstung wrote:
>> time has passed without the signal coming back. This results in the 
>> time server replying with stratum 12 (for example) after a while and 
>> ensures that everybody has the same time, although it might be wrong. 
>> If a user does not want that, they can simply set the local clock 
>> stratum to 15 and the server will not be accepted anymore.
>> Can you please let me know why you consider this a "bad implementation"?
> Because the protocol fails to signal the loss of the time source 
> properly when one has a local clock configured.  As such, I believe that 
> enabling a local clock should always be an opt in choice.  Basically, 
> when it falls back to the local clock, root dispersion goes to zero, 
> when the true situation is that root dispersion is growing without bound.
> Things can go seriously wrong if there is more than one local clock 
> source on a network, as it becomes possible for them to outvote the real 
> time.

Local clock IS an opt in choice.  If you don't configure it, it doesn't 
serve time.  Stratum is taken into account in selecting a time source.
I can't swear to it but I'd be surprised if three stratum 10 servers 
could out vote one stratum 2 server.

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