[ntp:questions] How to choose time servers
Richard B. Gilbert
rgilbert88 at comcast.net
Fri Oct 26 21:40:31 UTC 2007
Patrick Nolan wrote:
> I'm located at a university. We have a master Stratum 1 server with a
> GPS clock. We also have at least four Stratum 2 servers which are
> synchronized with the master. These are all very close, with delay
> and offset values less than 1. How should I use these resources?
> Should I put them all in ntp.conf?
No! If the stratum two servers are using only the University's stratum
one server as a source, they provide you with no diversity.
> Should I use only the Stratum 2 servers?
> Should I include one or more independent servers from somewhere else?
Yes. I would configure the University's stratum one server as one time
source and include at least three other independent sources! Four
independent servers are the minimum for a robust configuration.
Choose servers that are close to you in network space. A server in the
next room that is reachable only by a 3,000 mile path through several
networks is 3000 miles away for your purposes! Look for servers with
low values of delay; less than twenty milliseconds is okay, less than
ten is great!
Ntpd will probably select the University's stratum one server as its
primary source; the rest will serve as a sanity check and as a backup
should your stratum one server fail.
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