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<a class="moz-txt-link-abbreviated" href="mailto:gadgeteer@elegantinnovations.org">gadgeteer@elegantinnovations.org</a> wrote:<br>
<blockquote cite="mid20040822152509.GG4564@hyper" type="cite">
<blockquote type="cite">
<pre wrap="">Depending upon the criticality of the time sensitive applications on
the network, you might want to reconsider the use of "radio clocks"
and especially "GPS clocks".
</pre>
</blockquote>
<pre wrap=""><!---->[...]
For a fixed installation detecting if someone is dinking the gps signal
is trivial. The unit starts thinking it is not in Kansas anymore.
</pre>
</blockquote>
As far as I can remember, the gps is not accurate ... during US raids
(i.e. against Iraq) I could not tell if time is affected or if it only
reduce the precision over the location (50-20 meters during normal
operation, 100-1000 meters during raids). Anyway, I use a couple
internet & free ntp services (my ISP, some european & US labs,
...) If all the servers are compromised, I'm too (as far as time and I
are concerned, I want my whole network to be synchronized, I don't
really care for the real time, before configuring a remote ntp server,
there was only a 'virtual' time (my whatch), which was enough for my
logs), if only a few are, I can see there's a difference in the timing
they provide (which,anyway, I don't care about).<br>
<br>
In germany (which means anywhere between spain and russia), there is an
official radio-clock (known as dcf-77) which does not suffer the gps
limitation (this is not a military toy). As an official clock (used
for synching administratins, parking payments,... ) it have to be up
and give the official accurate time 24-7, You (or at least I) can be
confident with this time. Unfortunatly, most receivers do not work in
machine rooms (too many ecm noise, sometimes, the building is
radio-protected,...) you have to put your receivers (yes, one is not to
be concidered reliable) out of your building !<br>
<br>
These radio clock are easier to corrupt than gps (plain old fm against
spread spectrum)... I never faced any real time-critical project,so for
me (and I guess most admins), even the worst solution (internet NTP) is
more than enough right now (it may change in the future).<br>
<br>
Anyway if you consider this kind of solution (internet NTP), do not
forget ACL on your routers/firewalls, use a single/cluster ntp server
for synching your network, do not let multile servers sync with the
internet NTP.<br>
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