[ntp:questions] Re: Dopey selection of server

Richard B. Gilbert rgilbert88 at comcast.net
Sat Jan 31 18:40:24 UTC 2004

Christopher Burian wrote:

>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.?
>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.  
Welcome to Chimeheads Anonymous!  I think that "I care more than I 
should about what time it is." should become the first "tick" of our 
Twelve Tick Program.  ;-)

>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    2 u  767 1024  377  27.191 -28.007 0.225
>+filbert.cc.colu   2 u  752 1024  377  16.428 -23.531 2.738
>+cudns.cit.corne   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!  
Windows is far from my favorite operating system but I think that there 
is some tendency to blame it for everything from hemorrhoids to global 

NTP clearly knows that the local clock is roughly 25ms off.  It should 
be doing something about it. Specifically, it should be slewing the 
local clock to bring it into synchronization.

If it's maintaining that 25ms offset over an extended period, something 
is very wrong.  On the other hand, if a major change in network behavior 
took place very recently, it could be that NTP just realized how far off 
it is and will correct the offset over the next few minutes.

More information about the questions mailing list