[ntp:questions] NTP request retry?

detha detha at foad.co.za
Wed Jan 29 07:22:23 UTC 2014

On Tue, 28 Jan 2014 13:31:51 +0000, Charles Elliott wrote:

> Discussion:
> 	It is definitely, definitely true that offset (error) is highly
> correlated with the distance between the client and the server.  For a
> time, one of the stratum 2 servers in the USA State of New Jersey was
> using a server at a technical university in Poland as a source of time. 
> When the New Jersey server was connected to a server in New York (maybe
> 20-25 miles away), its time output was in sync with everyone else's, but
> when it was connected to the one in Poland, its time was ~30 ms slower
> than everyone else's.  Perhaps the time it took the New Jersey server to
> warm up its local DNS (or ARP???) to  access the IP address of the Poland
> server accounts for this error.  Nothing or no one else has been able to
> account for it. And I have checked the formulas for delay and offset in
> the RFC and in the implementation in NTPD dozens of times and can find no
> error (as long as the server and the client are relatively close (within a
> few years) to each other in time).

That sounds more like a case of asymmetrical routing. I have seen that
sort of behaviour in a case where path delay one way was ~40ms, and the
return path over 200ms.


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