Question on Loosely Synchronized Router Clocks

bmanning at bmanning at
Wed Sep 19 08:39:20 UTC 2007

 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...


On Tue, Sep 18, 2007 at 02:40:16PM -0500, Stephen Sprunk wrote:
> Thus spake "Xin Liu" <smilerliu at>
> >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 

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