[99320] in North American Network Operators' Group
Re: Question on Loosely Synchronized Router Clocks
daemon@ATHENA.MIT.EDU (Deepak Jain)
Mon Sep 17 18:27:07 2007
Date: Mon, 17 Sep 2007 18:22:12 -0400
From: Deepak Jain <deepak@ai.net>
Reply-To: deepak@ai.net
To: Valdis.Kletnieks@vt.edu
CC: Kevin Oberman <oberman@es.net>, Xin Liu <smilerliu@gmail.com>,
nanog@merit.edu
In-Reply-To: <22134.1190066541@turing-police.cc.vt.edu>
Errors-To: owner-nanog@merit.edu
Valdis.Kletnieks@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
