[ntp:questions] Problem with NTP multicast server configuration

Brad Knowles brad at stop.mail-abuse.org
Sun Jan 16 01:11:45 UTC 2005

At 4:47 PM -0600 2005-01-15, Larry Mills wrote:

>  - Two hosts (hosts X and Y) are configured as NTP multicast servers; each
>  server is a peer of the other, in symmetric-active mode.

	Use either one server or at least three.  Two servers is the 
worst possible configuration, see 

	Other than that, if you want the servers (and clients) to keep 
reasonably accurate time, you'd need to add an external refclock.

	A GPS with OXCO (Oven Stabilized Crystal Oscillator) would be 
ideal, but that would require a connection to the outside world, 
albeit not to the Internet.  Other alternatives of this sort would 
include a radio refclock (DCF77, CHU, WWV/WWVB/WWVH, etc...), a CDMA 
refclock, or even simple dial-up ACTS modem service.

	If you cannot have any kind of connection to an outside source, 
then you could have an OXCO or TXCO (Thermally Compensated Crystal 
Oscillator), and at least that would have less drift and less 
variation in drift than the standard CPU clocks that you have in your 

	But you really should read through all of 
<http://ntp.isc.org/bin/view/Support/DesigningYourNTPNetwork/>, and 
ideally also the rest of the stuff at 

	Of course, there's also the NTP FAQ at 
<http://www.ntp.org/ntpfaq/NTP-a-faq.htm>, and the official NTP 
documentation at 

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.

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