[ntp:questions] help in evaluating NTP servers performance

Richard B. Gilbert rgilbert88 at comcast.net
Mon May 14 13:54:01 UTC 2007

themule wrote:
> Hello,
> 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.
> TIA,
> .TM.

Well, your stratum two servers are obviously being "jerked around" by 
your network connection.  There's not much that you, or anyone, can do 
about it; networks, particularly the internet, are like that.

"Good enough" is usually enough.  If you need or want greater accuracy 
and stability, try getting a GPS receiver designed for timing service 
and use it as a reference clock.

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