[ntp:questions] help in evaluating NTP servers performance

themule marco.colombo at gmail.com
Mon May 14 12:49:38 UTC 2007

I have 3 servers operating at stratum-2, providing time to a small
population of clients (most routers and stratum-3 servers that
redistribute time to their LANs). The only source of time sync are
public NTP servers, and the configuration is based on this document:
http://www.eecis.udel.edu/~mills/ntp/html/notes.html. Each server has
2 stratum-1 sources (total of 6 distinct servers) and 4 stratum-2
peers (the other 2 internal servers plus 2 external ones). The reason
for this is mostly the ability to simple disable one external server
when it goes off-sync for some time and still have 3 external sources.

Now, I know that performance is quite a subjective matter. All we need
is to keep lan servers and clients in sync, with most timestamps
having 1 sec resolution. Currently I see offsets of about +/- 10ms on
ours main NTP servers, with occasional peaks, so let's say performance
is "good enough" for us.

But sometimes I wonder how good is that on an absolute scale, just out
of curiosity. And of course if it can be somehow improved. I've
plotted graphs from peerstats of the three main servers (ntp1, ntp2,
ntp3), and what really surprises me is that the three servers show
quite different patterns (hardware _is_ quite different tho).

May someone more experienced than me have a quick look at the graphs
and provide a couple of comments on them? They are here: http://stats.esiway.net/NTP/

I'd like to know how they compare to, say, similar stratum-2 servers.
I've found a few other graphs of running servers on the Internet, but
I can't make real comparisons since they are either stratum-1 servers
or stratum-2 servers right next (same LAN) to a stratum-1 server, and
of course their accurancy is orders of magnitude better.


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