[ntp:questions] Isolated Network Drift Problem

Cal Webster cwebster at ec.rr.com
Wed Nov 26 19:57:18 UTC 2008


Thank you for your detailed examples Steve. You have been very helpful.
I'm preparing to leave work for the Holiday weekend. If you are also a
US citizen, I'll wish you an enjoyable Thanksgiving Day.

./Cal

On Wed, 2008-11-26 at 18:06 +0000, Steve Kostecke wrote:
> On 2008-11-25, Cal Webster <cwebster at ec.rr.com> wrote:
> 
> > On Tue, 2008-11-25 at 21:10 +0000, Steve Kostecke wrote: [...]
> >
> >> > Unfortunately, connection to the Internet is not an option I'm
> >> > allowed to consider.
> >>
> >> Another option you could consider is the dumbclock driver. This uses
> >> a serial link to transfer time stamps from one system to another.
> >
> > Thanks but I'm afraid this would be of little use to me since most of
> > the systems are separated by brick and mortar, connected to each other
> > through DSL links on site.
> 
> This was a suggestion of a means of getting timestamps to the primary
> time server in your time island. Distribution of the time to other ntpds
> would occur over the network.
> 
> > So, if I wanted to setup my 4 NTP servers to look to the one with the
> > best local clock as the master (if you've been following this thread)
> > but fall back to Orphan mode when it became unreachable, could you
> > give me an example of how the configs might look? I could later point
> > them to the one with the GPS time reference as master when I get it
> > setup.
> >
> > My main concern is to continue to have an NTP server available in
> > each of 3 buildings even if they loose connectivity with each other
> > for some reason. I currently have at least one NTP service running in
> > each building, serving clients on MS Windows, Linux, and various Unix
> > flavors.
> 
> You need to set up the time servers for the orphan group in a "mesh"
> (i.e. they all need to poll each other for the time). You may use any
> NTP association mode for this purpose.
> 
> The following examples are incomplete; you need to add the drift file,
> any desired restrictions, etc.
> 
> *** Unicast:
> 
> # Master Time Server *
> # setting minpoll 4 makes this ntpd available to clients
> # approximately 50 seconds after startup
> server 127.127.1.0 minpoll 4
> fudge  127.127.1.0
> 
> # Bldg A Time Server
> tos orphan 10
> server master.server.ip.address iburst
> server bldg.B.ip.address iburst
> server bldg.C.ip.address iburst
> 
> # Bldg B Time Server
> tos orphan 10
> server master.server.ip.address iburst
> server bldg.A.ip.address iburst
> server bldg.C.ip.address iburst
> 
> # Bldg C Time Server
> tos orphan 10
> server master.server.ip.address iburst
> server bldg.A.ip.address iburst
> server bldg.B.ip.address iburst
> 
> If you have additional time servers create similar ntp.conf files and
> make sure that each servers knows about the others. 
> 
> *** Manycast:
> 
> This mode provides automatic server discovery and creates unicast
> associations. To use Manycast your server must be configured for to
> support Multicast addresses _or_ you need a site-wide broadcast address
> (i.e. every one on the same subnet). You also need to be comfortable
> with setting up symmetric keys.
> 
> One advantage to using Manycast mode is that you can drop in additional
> time servers without reconfiguring all of your existing time servers.
> 
> # Master Time Server *
> # setting minpoll 4 makes this ntpd available to clients
> # approximately 50 seconds after startup
> server 127.127.1.0 minpoll 4
> fudge  127.127.1.0
> manycastserver broadcast.or.multicast.address
> 
> # Bldg Time Servers
> # each "building time server" uses this file
> tos orphan 10
> manycastclient broadcast.or.multicast.address key N
> manycastserver broadcast.or.multicast.address
> 
> * Note:
> 
> I am suggesting the use of the Undisciplined Local Clock on your Master
> Time Server primarily beacuse The Undisciplined Local Clock has some
> "knobs" which may be used to interactively trim its performance through
> ntpdc. Orphan Mode, on the other hand, does not provide these knobs.
> 
> There is also a rootdispersion issue with Orphan Mode for stable
> releases up to 4.2.4p5 and for development releases before 4.2.5p101. I
> am currently conducting some tests.
> 




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