James Ray wrote:
On Mon, 12 Jun 2006 07:54:26 -0400, Richard B. Gilbert wrote:
James Ray wrote:
All,
Here is what we are after doing. Our networks team provides us with a
stratum 2 NTP server to use as well as our ISP providing us with 3
stratum 1 NTP servers. Ideally I would like a set of 4 peers run by me
syncing from the stratum 2 server provided on-site (since that gets it
data from the stratum 1 provided by the ISP) to reduce the load on the
stratum 1 servers. Unfortunately there are times when the on-site NTP
server goes a bit askew and steps out by up to 120ms (which isn't too
good for our uses).
I would choose to find out why the on-site server "goes a bit askew".
Machines running Linux or Windows have been known to lose clock
interrupts when busy. If your stratum two server is always slow when it's
off and "steps ahead" and is running Linux or Windows that is probably the
cause of your problem.
If that is the case, I would consider installing a better operating system
on the server; say Solaris 10 X86 or ever replacing the server entirely.
I've used Sun Ultra 10 boxes with Solaris 8 and Solaris 9 and find them
very well behaved. I've also had good experience with Solaris
8 and 9 (X86 edition) on PCs.
Unfortunately this machine is outside my control, its running FreeBSD I
believe. I could 'jump over its head' and just use the stratum 1 servers
provided by the ISP but I still suffer the main problem of flip-flopping
between the two servers when there are very small differences between them.
Free BSD should be okay. Knowing that it's BSD, I'd look elsewhere for
the problem.
You complain about clock hopping "between the two servers" but you said
there were *three* stratum one servers. Any NTP client using more than
one server will change servers from time to time as conditions
(primarily network conditions) change. This is a known problem and I
believe that the most recent version of ntpd has been fixed to reduce,
but not eliminate, this tendency.
If your needs are such that you cannot tolerate the small jumps in time
caused by "clock hopping", you need to rethink your design. If you can
site an antenna where it will have an unobstructed view of the sky, a
GPS timing receiver should give you an ultra-stable reference clock and
make your server stratum one. The Garmin GPS18-LVC costs about $85 US.
I use a Motorola Oncore M12+T receiver that I got, with the
"evaluation circuit board, for about $200. It works very well indeed.
The "estimated error" reported by ntptime is generally less than two
microseconds! I have some network servers configured as backup and
sanity check but ntpd is almost never forced to resort to them for time.
For a bit more money you can get a GPS receiver in a case with knobs,
switches, displays, or even a built-in NTP server. That last costs
quite a bit more.
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