[ntp:questions] NTP set-up when no external time source becomes unavailable?

Donat-Pierre Luigi luigi at ict.usc.edu
Fri Nov 4 02:16:02 UTC 2005

I am new to the list and from reading the archive I found that on Tue Oct 18, Marco Molteni posted a similar question.  First of all, I understand that NTP is meant to adjust system clocks to the best time from reference clock.

Our setup here is slightly different than Marco's.  It is a mobile three PC-cluster which is often without internet access for extended period of time, there is no external time reference such as GPS or atomic.
I am using the NTP daemon (precompiled) implementation ntpd on Debian and Windows NT.

The isolated network is composed of 3 hosts: A, B and C, where A and C are Debian Linux PCs and B is a Windows XP PC.

I tried to set-up NTP on B to use the local clock as a time reference (i.e. "Undisciplined Local Clock") when no external reference clock from the internet is reachable.  I used broadcastclient so that A and C can use B as their server.

(Note that I am not sure if I should use broadcast instead.  Besides I am not clear on how to define a broadcast server address, is it that of the system to use as reference, its IP address?)

The stratum on A and C is set to 14 and it is set to 13 on B.  That is to say, I used each local clock as fall back reference clock and used fudge to set the stratum with bias towards B.

After several attempts at debugging and reading NTP documentations and feeling really confused, I can't prevent A and C to drift away without converging or stabilizing (i.e. with a stable offset) with the clock of the Windows XP PC B.

I would appreciate if someone could send me an example of ntp.conf for both the clients (the two Linux PC A and C) and the server (Windows XP PC)?

I would still like PC B to use up to four external servers (as recommended) whenever it has a network connection.  What is important to me is that the Cluster PCs have a small time difference between themselves - i.e. synch together.  That is to say, the accuracy of the absolute time is not as essential, it just need to be reasonable within seconds.

Also, what I would really like is that the two Linux PC (A and C) display the minimum time offset with respect to each other. 
Shall I configure A and C to peer with each other so that each clocks minimize the relative error with the reference clock from B?

I look forward to receiving some suggestion and ideally the two ntp.conf files I need to use as a model for this less than ideal time management.

Many thanks in advance for your help.

Donat-Pierre LUIGI, Ph.D. 

Research Associate 
Institute for Creative Technologies 
University of Southern California 
13274 Fiji Way                          desk: 310-574-1620 
Marina Del Rey, CA 90292          fax: 310-574-5725 

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