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Re: [OM] Somewhat OT: Computer Clock Management

Subject: Re: [OM] Somewhat OT: Computer Clock Management
From: Scott Gomez <sgomez.baja@xxxxxxxxx>
Date: Sat, 16 Aug 2014 19:25:22 -0700
Best practice is to get time sync from the nearest time server to you, and
not query the "source" directly for it. Time servers have a hierarchy, like
DNS servers, because of loading issues, and as turns out, most of the major
ISPs seem to provide this service from their DNS servers. Then you set one
machine in your network up to query the time servers directly, on fairly
long interval, and set all other machines on your network to query your
configured master machine. That's probably the best method for the average
person wanting accurate time service. Another way to do it would be to set
a network switch, or your router or firewall to be the master time server
for your home network, and point all other devices to it for time service,
where possible.

Note that upper level time servers can and will block connection from
devices they determine to a) poll too often, b) not be sufficiently high in
the hierarchy to poll high-level servers directly, or c) be sending
malformed queries. Whether you know if you've been blocked is entirely up
to you to determine, which, on Windows machines, often meant not knowing at
all until you started getting bizarre behavior on downstream machines due
to being too far out of sync.

Microsoft run a time server for the purpose. There are also ntp pool
servers that can be queried. See the (many!) notes and instructions
available via searching on "network time protocol" or "network time
service", but keep in mind that when it comes to use of critical internet
services like ntp, adherence to the RFCs are usually the "law" as far as
responsible system administrators are concerned. Relevant RFCs are numbers
958, 1305 (version 3) and 5905 (version 4). Unlike application programmers
(who have quite accurately been referred to by Chris Trask as "cyber
toddlers") responsible for the user-facing software, Syadmins (like myself,
for instance) are a famously cranky lot, and tenacious in their pursuit of
up-time. See XKCD, here:

http://www.xkcd.com/705/

or the BOFH series:

http://bofh.ntk.net/BOFH/

In our defence, I will say that we come by our reputation honestly.

Microsoft's note on use of Windows Time Service (which has been provided as
part of Windows since the XP days):

 http://support.microsoft.com/kb/307897

Properly set up, it's accurate enough for most uses (including sniping bids
on Ebay, which I often used to do). It has been a long time since I delved
further into it, but I believe some versions (probably newer than XP?) even
have a means of compensating for drift rate, which is usually the largest
error factor in home PCs, which aren't notoriously stable when it comes to
time. NOTE: there are significant differences in setup between "flavors"
such as XP Home and XP Professional. I would assume that that's true as
well for WinVista, Win7, and Win8.

Linux machines (and by extension, Macs, which use a very similar method)
are quite easy to configure to get time sync from a network source,
unless/until one needs extremely high accuracy. As far as I know, both have
a check box where it can be selected, and from then on it's usually
"automagic".

---
Scott


On Fri, Aug 15, 2014 at 11:02 AM, Chris Barker <ftog@xxxxxxxxxxxxxx> wrote:

> Thanks for more useful information, Ken.
>
> But you needn't worry about us in the UK: we get all our time from Big
> Ben, which is always on time.
>
> :-)
>
> Chris
>
> On 15 Aug 14, at 16:37, Ken Norton <ken@xxxxxxxxxxx> wrote:
>
> > Like seriously!  Take a frequency band meant for Space-to-ground
> > transmission, immediately next to the GPS band (where the signal
> > strength is somewhere just above the universe's noise floor) and
> > instead repurpose it to ground-to-ground transmittions with high power
> > transmitters. It wasn't just cheap, inexpensive unfiltered GPS units
> > that suffered. During the tests, it was wiping out everything and the
> > GPS BITS clock receivers were getting completely toasted. But that
> > didn't influence the regulators. It took the threat of airplanes
> > falling out of the sky before anybody would listen. We faced
> > opposition that was mind-boggling.
> >
> > In almost every case, the NTP sites you are getting your clock updates
> > from are primary timed from a GPS timed BITS Clock system.
>
> --
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