[ntp:questions] ntp ports

Richard B. Gilbert rgilbert88 at comcast.net
Mon Nov 10 02:14:38 UTC 2008

Melanie Pfefer wrote:
> Hi
> What ports need to be opened if my ntp servers are inside a firewall?
> thank you

Port 123.  But only if you need to query outside servers or serve time 
to systems outside the firewall.  If you purchase and install a hardware 
reference clock, such as a GPS timing receiver, you can dispense with 
access to servers outside the firewall.  This is an option reserved for 
the utterly paranoid!  Normally you would use one or more outside 
servers as a backup and sanity check.

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