[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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