[ntp:questions] Broadcast server with external one

Dave Hart hart at ntp.org
Tue Jul 10 16:26:29 UTC 2012


On Tue, Jul 10, 2012 at 08:58 UTC, Glencu Glencu wrote:
> There is a PC which acts as broadcast server for my subnet AND as unicast
> client which points to external server. Everything works ok and my question
> is rather theoretical. So, I'm killing the connection with external server
> and I'm getting two results:
>
> 1. If external server is working for some single minutes ( like 20
> minutes)- I synchronize PC and then I kill the connection the brodcast
> server stops to send the packets
>
> 2. If external server is working for longer period of time (like two days)
> - I synchronize PC and then I kill the connection the broadcast server does
> not stop to send packets - it even does not do that after one or even two
> days.
>
> I would expect that in second case server would also stop to broadcast. Am
> I right? I think it has something common with external server stabuility.
> Sorry, If the topic was already covered. I couldn't find it anywhere.

I don't understand the difference you're seeing between the two cases
unless the broadcaster has never synchronized before the external
server becomes unreachable.  You can tell it's never been synchronized
if "ntpq -c rv" output includes "leap=11".

In the second case the behavior you're seeing is correct.  The
broadcaster's root dispersion will increase so long as it is unable to
reach its source(s).  It's up to the broadcaster's clients to decide
how much root dispersion is too much and rule it out.  The default for
ntpd is 1.5 seconds and can be customized with "tos maxdist":

http://www.eecis.udel.edu/~mills/ntp/html/miscopt.html#tos

Cheers,
Dave Hart


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