"Richard B. Gilbert" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
Duplication is not particularly desirable but it's damned difficult
to avoid! Each peer needs a minimum of four time sources.
Providing four unique servers to each peer would require sixteen
servers. It can be difficult to find even four really good servers
for a site. There are many good servers out there but "good at the
server" is not the same as "good, as delivered here". The Internet
can really mess up the time as delivered at your site so the problem
becomes one of finding servers with low latency and stable round
trip delays.
Peers with more than one server do not just "track" one server. One
server is selected as the primary source and the remaining "usable"
servers act as an "advisory committee" having some small influence
on the clock. See the RFC or Dave's "slide show" for the math; I'm
sure the math is much more precise than my fumbling English
translation thereof.
Ok, so I've taken a kind of aggressive approach to getting an 'ideal'
setup. I used the list of public stratum 1 and stratum 2 clocks, and
pulled all US entries that are A) Open and B) don't request
notification. I've setup a dedicated box in my lab that does
aggressive (burst, low interval) polling of my 4 existing ntp time
sources, using them as a baseline. I've conf'd all the servers in the
list I generated, setting min/max poll to 12 (34mins) so I don't abuse
anyone. I've got a perl script going through and recording the
observed offsets, latency, and jitter using RRDTool and plan to try
and find 16 solid sources from that list.
I only have about 24 hours worth of data, but I've already spotted
three trends. First are servers that tend to report offsets very
close to what I'm getting as 'true' time from my 4 existing ntp
servers, one of which is tracking ACTS. The second is a group of
servers that all seem to have a systemic offset, but are otherwise
quite stable. The third are all over the map.
I know the third group is garbage, but what about the systemic offset
servers? I would think they would be usable to at least get frequency
info from despite the offset, or should I avoid them as well and start
contacting remote servers if I can't fill out my 16 slots using first
pick servers?
Joshua Coombs
_______________________________________________
questions mailing list
[email protected]
https://lists.ntp.isc.org/mailman/listinfo/questions
