[ntp:questions] Remaining synced on an unsynchronised peer?

Michael Butow michael.buetow at comsoft.de
Mon Nov 30 22:46:41 UTC 2009

On Mon, 30 Nov 2009 17:12:51 -0500, Richard B. Gilbert wrote:

> Are you aware that two servers is the worst possible configuration?  It
> is written that a man with two clocks can never be certain what time it
> is.  Four, five, and seven are the magic numbers of servers required to
> survive the failure of one, two, and three servers respectively.

Yeah, that's understood, it was just an example config I used above.
I am fairly sure my problem exists regardless of how many external 
servers are configured (I've reproduced it with two and three).

Speaking of magic numbers: aren't even numbers disadvantageous because 
they can be split by the NTP algorithm into two groups, and then it 
becomes a gamble to pick which groups to believe? 
I've heard it said because of that one should pick an odd number of 
servers, and always wondered if there was some truth to that.

On the possibility of my problem being an NTP bug, I presume I have to do 
some triaging with different NTP versions, to see if maybe newer NTP 
releases fix this magically (haven't seen a bugfix in the ChangeLog which 
I could correlate to it).

So, unless I get input from someone who can certainly contradict my 
expectations, I'll assume it's a bug.

More information about the questions mailing list