[ntp:questions] Problem syncing NTP behind NAT

Dave Hart hart at ntp.org
Sat Apr 7 21:36:36 UTC 2012

On Sat, Apr 7, 2012 at 16:53, Ken Link <klink at numberzero.org> wrote:
> I did some more testing with a total of four different machines behind
> the NAT. Two of them synced in a few seconds, the other two were stuck
> in INIT. For the machines that didn't sync, the external server did
> not respond at all.

I notice the successful clients were querying using ports > 123, and
the failing ones < 123.  I dimly recall seeing an inappropriate
less-than-123 source port comparison in ntpd long ago, in fact I'd
have guessed it had been removed before 4.2.6p3.

I suggest trying a newer ntpd outside the NAT, or if possible
reconfigure the NAT to avoid low source ports.

Dave Hart

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