[rhn-users] ntp parameter to reduce update interval

[Jesse Becker]

On Wed, Apr 06, 2005 at 12:04:36PM +0200, cbeerse at gmail.com wrote:
> ========
> ##
> # A list of available servers can be found here:
> # http://www.pool.ntp.org/
> # http://www.pool.ntp.org/#use

Those are public pool servers.  You don't have to use them (if you have very
strict firewall rules, for example.  Naturally, it's best to have all of
your computers have the "correct" time, but having everything consistantly
incorrect (say, everyone is 23 seconds slow) is better than nothing.

That said, sync one of your local boxes to several pool servers, and then sync
your other local boxes to that one.

> ##
> #server pool.ntp.org
> server pool.ntp.org minpoll 15 maxpoll 17
> ========
> 
> The server is polled regularly, starting at every 2^minpoll seconds. Once 
> the time is in sync, the poll time is extended up to every 2^maxpoll 
> seconds. I don't know the defaults by head, as far as I see my machine, 
> maxpoll is 10, resulting in a poll every 1024 seconds.

The defaults are:
	minpoll = 6   (2^6 = 64 seconds)
	maxpoll = 10  (2^10 = 1024 seconds)

Valid ranges are 4 (sixteen seconds) to 17 (well over 36 hours).

Another way to do this is use a multicast or broadcast setup for NTP packets.
On your NTP server, add a line like this:
	
	broadcast 1.2.3.255 

Replace "1.2.3.255" with the broadcast address of your subnet.  You can set
maxpoll to adjust how often the NTP server will send updates.  I am not sure
of the exact behviour of minpoll in this context.

On the NTP clients, these two lines should work:
	
	restrict 1.2.3.0  mask 255.255.255.0
	broadcastclient

Replace "1.2.3.0" with your *subnet* address (not broadcast), and set the
netmask appropriately.

I am omiting a number of authorization and security things (auth keys, and
restrict lines, as you should set those up as appropriate for each site.


-- 
Jesse Becker
GPG-fingerprint: BD00 7AA4 4483 AFCC 82D0  2720 0083 0931 9A2B 06A2
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