[ntp:questions] Re: Passive client?

Richard B. Gilbert rgilbert88 at comcast.net
Wed May 24 14:46:09 UTC 2006

Collins wrote:

> I have been reading the ntpd man pages and other documentation at the
> iesc but I have yet to find an explicit answer to the following
> question.
> Is it possible to configure a client so that it never attempts any
> communication with a server but simply monitors a multicast group for
> updates?  If so how?
> A possibly related question: what is the behavior of ntpd if it is
> started with a configuration file which specifies no servers?
>   Thanks in advance
>     Collins

I don't believe it's possible.  Ntpd needs to exchange packets even when 
acting as a broadcast or multicast client.  That is necessary to 
establish a value for the round trip packet delay.  Once the client 
determines the delay, it will shut up and listen.

I've never tried starting ntpd without any servers.  It's just one of 
those things that never occurred to me as a sane or useful thing to do. 
  If the designers considered the case at all, they probably had the 
code exit; there is nothing useful that it could do without at least one 
server.  If, OTOH, ntpd loses contact with all its servers it should 
continue to discipline the local clock using the last available data.

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