[ntp:questions] Fudge time offset on client/peer?

Danny Mayer mayer at ntp.org
Sun Nov 8 00:26:08 UTC 2009


Can we not just introduce an option on the server line for this? That
would effectively give you the association. The caviat here is how do
you know what to put in the argument?

David Mills wrote:
> Rich,
> I have the same situation you have, but a dedicated ISDN line and 
> routers that have a mostly symmetric delays. A per-association fudge is 
> not possilbe unless the peer mobilization code is overhauled. There is 
> in fact a calibration mechanism designed to compensate for small 
> inconsistencies using the PPS signal as the ultimate reference. That is 
> controlled by the enable/disable calibrate command and applies to all 
> associations. A command might be introduced that could affect a 
> specified association, but it would have to be given via ntpq after 
> mobilization.
> Dave
> Rich Wales wrote:
>>> I suggest you don't want that.  What you need is a fudge on the
>>> interface, not the association.
>> In this situation, I think I really do want a fudge on the association.
>> Consider the issue from the POV of my work desktop.  My work desktop
>> has a single network interface, connected to a conventional 100BASE-TX
>> ethernet network.  It has fast (and, for my purposes, sufficiently
>> symmetric) connectivity over my school's campus network to stratum-1
>> and stratum-2 servers run by the campus IT services.
>> In order for my work desktop to see the stratum-1 server I'm running at
>> my home, however, it has to go over the campus network to the cable-modem
>> network servicing the townhouse complex where I live.  As I previously
>> mentioned, this cable modem network appears to have an asymmetry, which
>> I would like to fudge away for the benefit of my work desktop (but *not*
>> for my home LAN).
>> If I were to fudge the network interface of my work desktop, this would
>> presumably affect not only its view of my home stratum-1 server, but also
>> my work desktop's view of the campus tickers.
>> What I think I want/need is a way to fudge my work desktop's view of one
>> peer/server, but not another peer/server.  That's why I wanted to be
>> able to fudge an association.
>> Rich Wales  /  richw at richw.org
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