[ntp:questions] NTP and NAT

Maarten Wiltink maarten at kittensandcats.net
Thu Nov 8 08:46:12 UTC 2007

"Daniel Guerrero" <dguerrero at ttrends.es> wrote in message
news:5587B1EB0BF882418007350B60425C838E0CE9 at techno1.intranet.techno.com...
> I'm a newbie on NTP, and i would like to know if there is any problem in
> configuring more than one machine with the same NTP server on a LAN that
> connects to the internet through a NAT (with the same outgoing IP for
> everyone).

This is not so much an NTP question as a NAT question.

The usual type of NAT works on UDP and TCP because they have source ports.
The original source IP address and port are remembered along with the
translated source IP address and port (on the gateway), and when traffic
comes back to the translated source IP address and port, the gateway knows
where the original packet came from, and forwards the return packet to
that same place.

So yes, it will work fine. But you can save a hop and all the translating
by running NTP un-NATted on the gateway. (And the gateway was in fact the
only place anyone ever questioned my logging timestamps.) Of course, if
the gateway came out of a blister pack, this may not apply.

Maarten Wiltink

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