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