[ntp:questions] Let ntp server not synchronize time from other servers

Kevin Oberman oberman at es.net
Thu Aug 28 17:37:34 UTC 2008


> From: Steve Kostecke <kostecke at ntp.org>
> Date: 28 Aug 2008 15:25:31 GMT
> Sender: questions-bounces+oberman=es.net at lists.ntp.org
> 
> 
> On 2008-08-28, WANG Cong <xiyou.wangcong at gmail.com> wrote:
> 
> > On Aug 28, 12:49 pm, "Maarten Wiltink" wrote:
> >
> >> server 127.127.1.0
> >> fudge 127.127.1.0 stratum 14
> >
> > Cool! It works! 8-) But there's a little problem, when I changed my
> > ntp.conf, I have to wait for several minutes until it works well, if
> > not, I got:
> >
> > 192.168.90.41: Server dropped: strata too high
> >
> > I googled a bit, and someone said this is due to the time of the
> > server is far from correct, but it is not. See below:
> 
> No. That's not the problem.
> 
> Your server needs to be "synced" before ntpdate will consider it
> acceptable. The issue here is that with the configuration suggested
> above the current stable release of ntpd will take almost 3.5 minutes
> before it decides that it is "synced". This is because the default poll
> interval is 64 seconds and ntpd requires 3 poll periods before it
> accepts the Undiciplined Local Clock.
> 
> You may speed this process up by reducing the minpoll to 4. This sets
> the minumum poll to 16 seconds and reduces the "sync" time to ~ 50
> seconds.
> 
> If that is not fast enough try the current ntp-dev snap shot which,
> IIRC, accepts the Undiciplined Local Clock after the first poll.
> 
> You may also want to try Orphan mode instead of the Undisciplined Local
> Clock on your "server". Enable orphan mode like this:
> 
> 	tos orphan N
> 
> Where 'N' is the stratum that you want your server to operate at. It is
> considered good practice to use a large number (e.g. 10, or so) to
> prevent problems when your time-island is connected to other networks.
> 
> >> Is there any particular reason why you won't take the time from
> >> anyone?
> >
> > Yes, because we want:
> >
> > 1. Configure the time of the server manually, no matter how wrong it
> > is. :) So in this situation, we don't want synchronization, but still
> > need to provide the time service to other PCs.
> 
> Why do you need to do this?
> 
> Please keep in mind that NTP is designed to synchronize computers to
> a common time-base. UTC (via WAN, LAN, or directly attached reference
> clock) is ubiquitous time-base because, but other time-bases may be
> used. NTP is not a magic black box which can produce stable clocks with
> out some sort of stable (usually external) reference.
> 
> > 2. Synchronize the time from other servers and provide service. This
> > is very easy and works well.
> 
> That is what NTP is designed for.

While I'm not at all sure that this is what is wanted, if ntp uses
systime_s.c instead of systime.c it will run ntp without ever looking at
or adjusting the system time. Just edit the Makefile for libntp to
change systime.c to systime_s.c in NTP_SRCS.

systime_s.c is the "simulation mode" version normally used in
development and debug.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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