Re: ntp/ntpdate and NAT

[Martin Husemann <martin%duskware.de@localhost>]

On Tue, Jun 04, 2013 at 03:05:21PM +0200, tlaronde%polynum.com@localhost wrote:
> The question arised because I have bad values (more than 2 seconds
> offset) for a node on which I have made a "ntpdate -b" (so no adjtime) a
> day before: the (new, dual-core x86_64, NetBSD 6.1) PC clock is not an
> atomic clock, but when the system is running it does not shift by
> several seconds a day, or is it?

If your NAT device causes persistent enough packet handling delays in the
order of 2 seconds (or enough to make NTP erroneously drift that far),
you have a serious problem.

I have a few machines behind a NAT that sync very well with an external
NTP server, typical ntpdc -s looks like:

     remote           local      st poll reach  delay   offset    disp
=======================================================================
XXXXXXXXXXXXXXXX xxxxxxxxxxxxx    3 1024  377 0.04420  0.006242 0.13820


What timecounter source did your machine pick and what other choices do you
have?

        sysctl kern.timecounter

should tell you.

Martin