[ntp:questions] Re: Dopey selection of server
Richard B. Gilbert
rgilbert88 at comcast.net
Fri Jan 30 13:09:34 UTC 2004
I've experienced the same thing. I was told that NTP was working as
designed. I guess I just don't understand the design! Intuitively, it
would seem best to select the server with the lowest delay and jitter
but that's not what it does. If cudns.cit.conrell.edu consistently
shows high delay and jitter, you might want to look for another server.
Server selection is, I think, a bit of an art. Servers that should be
superb are, in fact, terrible due to server or network overload; e.g.
the various NIST servers. I know of a stratum two server that drifts
+/- 20ms over the course of the day and I know of others that are rock
solid! Unfortunately, the rock solid and apparently dead accurate
servers are difficult to find. And what might be rock solid and dead
accurate for me could appear totally useless to you due to us reaching
it by totally different network paths. There are only about 100 stratum
2 servers open to the public and another 100 or so open stratum 1
servers. Servers that are too distant are generally not very good ones
to use; based on your choice of servers I'd guess that you are probably
in or near New York state.
Servers in Florida, California, or Europe would have high delay and
jitter for you but might be ideal for local users.
I'm trying to get a stratum 1 server working in my home to avoid some of
these problems. Unfortunately, my contract with Comcast appears to
prohibit my making it publicly available.
Christopher Burian wrote:
>Can anyone explain this:
> remote refid st t when poll reach delay offset
>+cs.columbia.edu 188.8.131.52 2 u 725 1024 377 16.819 -7.688
>+filbert.cc.colu 184.108.40.206 2 u 704 1024 377 22.523 -4.356
>*cudns.cit.corne 220.127.116.11 2 u 656 1024 377 60.335 13.325
>Instead of rejecting the one that is off the most from the others, it is
>selecting that wayward server, despite it having the worst jitter as well.
>Is the selection based on a longer time frame, and I just happened to pick
>a bad time to look at how it's doing?
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