[ntp:questions] Re: NTP sync on a standalone network (Windows 2k)

David Woolley david at djwhome.demon.co.uk
Sat Aug 19 10:45:18 UTC 2006

In article <v9ydnV8UkcY2yHvZnZ2dnUVZ_qqdnZ2d at comcast.com>,
Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> Alexandre Carrausse wrote:

> > I agree but the link between the GPS antenna and the secure area will be 
> >  coper, not fiber.

No.  The copper would terminate on the GPS receiver, which would be outside
the secure area.  The fibre would carry the baseband NMEA signal.
> If you are allowed to have a fiber optic link but not a copper link you 
> could run NTP over the fiber link!  I'm not aware of any refclock that 

There are two likely reasons for restricting to fibre: one is EMP 
protection, the other is security.  If security is the case, and
you operate a bidirectional protocol like NTP, the electronics at the
remote end of the link would almost certainly also be considered 
part of the secure area and subject to the same restrictions as the 
main area, unless the data was encrypted and they were not the final
end point of the transmission.  (Google "covert channels" for more.)

He might be allowed to operate a link that was uni-directional, which
would allow him to have the complete receiver in an insecure area,
and transmit the data optically (phototdiodes aren't very good light
sources, so there is little risk of information leaking the other way).

I don't believe that ntpd needs to be able to talk to NMEA time sources,
although it may try to configure them.

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