[99352] in North American Network Operators' Group
Re: Question on Loosely Synchronized Router Clocks
daemon@ATHENA.MIT.EDU (bmanning@vacation.karoshi.com)
Wed Sep 19 04:40:41 2007
Date: Wed, 19 Sep 2007 08:39:20 +0000
From: bmanning@vacation.karoshi.com
To: Stephen Sprunk <stephen@sprunk.org>
Cc: Xin Liu <smilerliu@gmail.com>,
North American Noise and Off-topic Gripes <nanog@merit.edu>
In-Reply-To: <04e201c7fa77$c08125d0$6601a8c0@atlanta.polycom.com>
Errors-To: owner-nanog@merit.edu
top posting to keep you alert!
there are folks who syncronize clocks so that logs make sense.
and those that do, tend to pick a common TZ... there is nothing
like syncronizing logs from routers in Nepal, India, China, and LA
UTC can be your friend...
wrt acces to clock source - i'd be happy to have the httpd server
code pulled out and adding a GPS/802.11 timesource to the platform
of joy. of course presuming that a router clock is ammenable to
an external discipline source. Many PC's are not...
--bill
On Tue, Sep 18, 2007 at 02:40:16PM -0500, Stephen Sprunk wrote:
>
> Thus spake "Xin Liu" <smilerliu@gmail.com>
> >Sorry for the confusion. Let me clarify.
> >
> >We are interested in a number of questions:
> >1. Can we assume loosely synchronized router clocks in the
> >Internet, or we have to make absolutely no assumption about
> >router clocks at all?
>
> That assumption is _generally_ true, but not often enough that you can rely
> on it.
>
> >2. If the router clocks are indeed loosely synchronized, what is
> >the granularity we can assume? Particularly, we are interested in
> >whether we can assume router clocks are synchronized within
> >10 minutes.
>
> My experience is they'll either be within a few seconds or off by several
> days to years. There's not much middle ground.
>
> >3. It's always possible that a router's clock goes wrong. In
> >practice, how often does this happen?
>
> It's unlikely to "go wrong" to any noticeable degree _if it was ever
> correct in the first place_. However, many people do not bother setting
> the clocks at all (which will often result in a clock that's off by a
> decade or more), or intentionally set them to be wrong. A lot of folks had
> to set their clocks back a few years around Y2k, for instance.
>
> S
>
> Stephen Sprunk "God does not play dice." --Albert Einstein
> CCIE #3723 "God is an inveterate gambler, and He throws the
> K5SSS dice at every possible opportunity." --Stephen Hawking
>
