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

Steve Kostecke kostecke at ntp.org
Thu Aug 28 15:25:31 UTC 2008


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.

-- 
Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/




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