[ntp:questions] Can't Understand NTP behaviour,

David Woolley david at ex.djwhome.demon.invalid
Tue Jun 28 07:07:18 UTC 2011

Pranay Kumar Srivastava wrote:
> In our NTP client-server setup which is done locally, we've 3 servers each made to synchronize with its own local clock only.

If you have more than one free running server (synchronised with local 
clock really means not synchronised at all, but claiming to be), it is 
unlikely that the error bounds for them will overlap.

In your case, you have about 140 microseconds of error bound due to 
potential network asymmetry, and there will be a few  milliseconds added 
for other reasons, but the times differ by 100s of seconds.  There are 
therefore no two clocks that could possibly be reflecting the same 
underlying time.

If you must run a free running system, you must have exactly one free 
running machine, and then synchronise everything else to that.  That 
means either one machine configured with the "local clock" as a pseudo 
source, or none, but using orphan mode to select one source.

> The contents of this e-mail and any attachment(s) are confidential and intended for the named recipient(s) only.

Not if you post them to a public mailing list, gatewayed to a usenet 
group.  Why should anyone believe future postings in more marginal 
circumstances are confidential?


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