[ntp:questions] Re: Dopey selection of server

Christopher Burian cburian at ll.mit.edu
Sat Jan 31 16:38:37 UTC 2004


Fred <junkmail at falseticker.co.uk> writes:

> On Fri, 30 Jan 2004 10:05:43 -0500, "Christopher J. Burian"
> <cburian at ll.mit.edu> wrote:
> 
> > At home, I ran that windows utility that
> >graphs ntp servers (mentioned a week ago here on the list) with 8
> >servers stratum 1 or stratum 2, and after a day (too short?) decided on
> >three stratum 2 servers.
> 
> I must have missed the reference to this windows utility - can you
> provide the link or message reference.?

http://www.david-taylor.pwp.blueyonder.co.uk/software/net.htm

Based upon advice, I added a fourth server, so that voting can work
properly.  But I forgot that I can't use a stratum 1 if the others
are stratum 2.  So I need to find a nice fourth stratum 2 public
server.  I've read the documentation and rationale (admittedly 
skimming over some of the math), and I can find no justification
for strictly preferring a stratum 1 over a stratum 2, rather than
perhaps using perhaps a weighted bias, not an overwhelming bias.  
Also, I don't see any reason why users shouldn't be able to fudge
a server's stratum to another level.  But these aren't my real
problems.  My real problems are: this is a Windows machine, and
I care more than I should about what time it is.  

How the following occurs is beyond me:
This is about 8 hours after restarting the driver.  I can only assume
that when ntpd happily runs 25 ms off from all its servers, it is 
because of Windows XP and not because of the software.  Or, could
it be due to asymmetric delay over cable modem?

ntpq> pe
     remote           refid    st t when poll reach delay  offset jitter
========================================================================
+cs.columbia.edu 204.123.2.5    2 u  767 1024  377  27.191 -28.007 0.225
+filbert.cc.colu 128.59.39.48   2 u  752 1024  377  16.428 -23.531 2.738
+cudns.cit.corne 192.5.41.209   2 u  762 1024  377  23.347 -22.800 1.811
*nts200.cs.umb.e .GPS.          1 u  742 1024  377  33.255 -24.702 0.260

None of these bad things happen on my Trimble- and Praecis-based
private networks running Linux.  On my system at work, I routinely
see offsets of 10s of microseconds.  Again, there, though, I am
very annoyed that I apparently cannot use a stratum 2 server as 
the primary server with a stratum 1 as a fallback if the primary
goes quiet.  Should be able to fudge the stratum 1 to stratum 2
in clients so that they will obey my prefer tag.  Or, they should
just obey the prefer tag!  

Regards,
Chris



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