[ntp:questions] Re: two ntp servers
rancidmoth at yahoo.com
Wed Feb 22 03:27:45 UTC 2006
thanks for the advice. I have opted to strip it all back and start again.
I did as you suggested and left on the server line in the config. and I
doubled checked every step. I also opted for a completely different
upstream server. this time the ntpq -p status seems more logical (i.e.
there is actually numbers in it rather than zeros). I also watched the
packets on the interface via tcpdump -ieth2 -p udp and ensured that this
upstream server was spitting back data that was reaching the interface. I
then made both servers have the same config and upstream data and va la!
they are now both exactly on the same time. I am now going through the
config to see if there is anyline in it that breaks this.
thanks to all for the tips, especially the ntpq -p
"Jed Clear" <clear at alum.mit.edu> wrote in message
news:43FA830D.B319B3D0 at alum.mit.edu...
> rancid moth wrote:
>> hello john
>> no it seems to definitely be reaching them. i have checked using the
>> dmpeers command. also running the ntpq -p i get the exact same thing as
>> what is on the other box. also note that in my trials i have set a
>> time from off the other machine and made them perfectly in synch. when i
>> then take that machine and point it to the upstream server it then drifts
>> until it is three minutes ahead. i just dont get it. odd dont you
> Could be something misconfigured in your ntp.conf that prevents ntp from
> actually setting the local clock, so it continues to drift. Auth can be
> tricky. Also I recall posts of an option that seems to have changed
> sense after a certain older ntpd version, but examples might not be
> I would start with a very simple ntp.conf:
> server ntp.yourISP.com
> and *nothing* else. If your ISP doesn't offer NTP (you might have to ask
> support desk), go pick an open stratum 2 off the wicki. Don't use the
> initially as your two servers could (should) get different servers for the
> name. If that works, add a bit of your current ntp.conf back in at a time
> it breaks. From what I've read here, you shouldn't be using minpoll and
> options at all.
> If you find you need to come back for more advice, those more
> knowledgeable than
> myself could probably help more if they knew what version of ntpd you're
> and what's in your ntp.conf.
>> "John Pettitt" <jpp at cloudview.com> wrote in message
>> news:43F4FDCA.3070402 at cloudview.com...
>> > 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.
>> > John
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