[ntp:questions] Re: NTP sync problems
Richard B. Gilbert
rgilbert88 at comcast.net
Thu Dec 9 22:24:59 UTC 2004
Robert Rati wrote:
> I'm running NTP 4.2 on a Linux system which syncs off of 2 other Linux
> boxes (One Debian, other Redhat) running ntp (one is ntp 4.1, other is
> ntp 4.1.2) and I'm having no problems syncing.
> However, when I use the same client in a different environment which
> syncs off of a Sun box running NTP 4.2 or a SUSE Linux box running NTP
> 4.1, I can't sync. When I run ntpq, I see this:
> [root@ root]# ntpq -pn
> remote refid st t when poll reach delay offset
> *127.127.1.0 LOCAL(0) 10 l 31 64 377 0.000 0.000
> x<IP> .LCL. 1 u 35 64 377 0.272 -33.321
> x<IP> LOCAL(0) 11 u 44 64 377 0.416 735934.
> The "x" status means that it is a "designated falseticker by the
> intersection algorithm". What does this mean? Is this a client or
> server configuration issue? Can anyone give me some tips on how to
> debug this situation?
You have configured two servers which have wildly different notions of
what time it is. Both servers are serving their unsynchronized local clocks.
Two servers is the worst possible configuration! Ntpd knows for certain
that at least one of these two is "insane" and has every reason to
suspect that both are.
You can configure an isolated subnet with no external time reference and
it will synchronize to whatever single server you designate. It
probably won't give you close synchronization because the server is
almost certainly drifting as badly as, or worse than, the clients. It
should keep all the systems within a few hundred milliseconds of each
other but they will not necessarily have the correct time.
If you want the correct time and close synchronization, use either a
hardware reference clock (GPS receiver, WWV reciever, WWVB receiver,
etc.) or a group of external network servers that are synchronized to
such reference clocks. Four, or more, servers are recommended for
protection against "falsetickers", hardware failures, and network
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