[ntp:questions] Re: two ntp servers

John Pettitt jpp at cloudview.com
Thu Feb 16 22:33:46 UTC 2006

rancid moth wrote:
> hello,
> not being very familiar with the ntp protocol, and currently introducing 
> myself to it properly (i.e. have always used though never dug deeply into 
> it), i have established two ntp services on two different Linux machines. 
> Both ntp servers are pointing to the _same_ upstream server.  There is a 
> four minute difference in time on the machines.  Lets call them machine A 
> and B.  initially i established them to the same time, by synching B's time 
> from A which itself was synched from the upstream internet ntp server.  If i 
> then modify B's config to also synch from the same upstream source, B, given 
> enough time, will drift 4 minutes ahead of A.  Can someone please point me 
> to an introductory explanation as to why/how this can occur.
> cheers
> moth 

Basically your setup isn't working for some reason - if you do "ntpq -p" on both boxes you'll
probably see that one or both of them are not actually talking to the upstream.    As a general rule
you need at least four upstream servers for stability (see www.pool.ntp.org for how to get more
servers).  It's probably a good idea to peer the two local servers and then point them at diverse
(overlapping is ok) groups of upstream servers as this will give to a very robust setup.

If I had to guess I'd say that a firewall somplace is blocking the ntp packets.


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