[ntp:questions] how to configure ntp for conditional use of servers, depending on my LAN status?

Brian Utterback brian.utterback at oracle.com
Thu Jan 10 13:24:02 UTC 2013

You don't need to have the info in config 1, there is no point. If you 
are not on a network then ntp doesn't have any clients and you don't 
want it changing the clock.

The cleanest way to do the other two is to have two separate config 
files and restart ntpd with the correct config file depending on the 
network topology at the time.

However, you could just configure all the servers. The ntpd process will 
try to resolve the server names and will continue trying to do so 
periodically until it succeeds. It will then try to send packets 
periodically until it succeeds. So, when you are not on the right 
network the packets will just not get there.

On 1/9/2013 2:21 PM, dar8757 at eml.cc wrote:
> hi,
> i'm running ntp-4.2.6p5-3.10.1.x86_64 on linux/64.
> i've a question about proper configuration/use of fallback on a roaming
> laptop.
> the laptop boots to a no-network configuration.  connection is
> chosen/enabled as needed after KDE desktop launch ...
> i'd like to configure ntpd.conf so that
> (1) at machine boot, ntp starts up using the machine's local time, in
> the absence of network access.  i think i'd use this:
> 	server
> 	fudge stratum 10
> (2) once network connection is made, if my IP is on my local LAN
> (, then use my local LAN's time server.  for that,
> 	server   ntp-server-f.q.d.n  iburst prefer
> 	restrict ntp-server-f.q.d.n
> (3) if my IP is not on my LANB, then use some external servers.  e.g.,
> 	server clock.isc.org             iburst prefer
> 	restrict clock.isc.org
> 	server ntp1.sf-bay.org           iburst
> 	restrict ntp1.sf-bay.org
> i'm not sure if/how to implement this conditional fallback 'logic' for
> ntp's server selection.  reading the docs, i think stratum can be used
> -- but really am not certain.  thought i should check before abusing
> some servers inadvertently.
> any guidance would be appreicated!
> thanks,
> daryl
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