[ntp:questions] ISP bloked port 123

unruh unruh at invalid.ca
Tue Sep 17 02:29:08 UTC 2013

On 2013-09-16, Bert G?tterup Petersen <BUP at bang-olufsen.dk> wrote:
> Well we see different issues in different countries.
> The problem that I am in the development department, but the individual customer issue happens in the field somewhere fare away and handled by people how understand little about IT...
> I am looking for a generic 'plan B' which will solve these different issues all at once, not one by one.

Servers listen on port 123. Thus if you want a server to actually listen
to your request for time, you have to deliver it on a port that they are
listening to-- port 123. So, if they are blocking outbound 123 you are
SOL. Now they may block inbound port 123, so that your machine cannot be
server to others ( on the argument that ntp servers can get huge amounts
of traffic.) So, which are they blocking?

If outbound you could set up a server of your own (say on port 80 say
which noone ever blocks) and have your own machines use it. 
You might have to recompile ntpd to use the new port.

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