Question on Loosely Synchronized Router Clocks

Deepak Jain deepak at ai.net
Mon Sep 17 22:22:12 UTC 2007



Valdis.Kletnieks at vt.edu wrote:
> On Mon, 17 Sep 2007 14:28:45 PDT, Kevin Oberman said:
>> I had a router that lost it's NTP servers and was off by about 20
>> minutes. The only obvious problem was the timestamps in syslog. (That's
>> what alarmed to cause us to notice and fix it.)
> 
> Trying to correlate logfiles with more than a several-second offset is
> good and sufficient reason in itself to make sure everything is NTP-synched.
> 

So to bring the conversation to something more sequitur and relevant.

1) Its not hard <tm> to keep all of your devices in your network sync'd 
to the same clock. Especially if you use standardized configuration 
control.

2) And a reasonable number is on the order of seconds (or ~1 second) 
rather than minutes which is almost the same as being unsynch'd.

3) It is not guaranteed, but not hard to be sync'd to a level of 
precision on the order of a second or two using globally-available NTP 
sources to every other network you might directly connect with.

I'm slightly suspicious of all the CDMA/atomic clock other NTP sources 
(for "higher precision") people point their IP gear at -- simply because 
IP doesn't need the same level of precision as SONET, at least, not yet.

[exclusions for my suspicion include any NTP sources I run, but that's 
merely hubris ;)].

Deepak Jain




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