Configuring a Stratum 3 Server
NB The example configuration files below are just that: examples. Please do not just copy them willy-nilly. If you have problems selecting a random machine roll a die!
There are four stratum 2 servers in the University you can use. These have the DNS aliases:
If you are setting up a single stratum 3 server for your system, pick a random three of these to be your servers. In this case your
/etc/ntp.conf file could be as simple as this:
driftfile /etc/ntp.drift server ntp1.cam.ac.uk server ntp2.cam.ac.uk server ntp3.cam.ac.uk
If you are setting up a set of servers for your department, you should select different sets of three for each server. You should also "peer" the departmental servers off each other. Two NTP servers are peers when each is prepared to provide time service to the other and is suitable for machines that are expected to be at the same stratum. This provides a degree of extra redundancy in your NTP provision.
If your departmental servers were
gamma.dept.cam.ac.uk then their
/etc/ntp.conf files might look like this:
driftfile /etc/ntp.drift server ntp0.cam.ac.uk server ntp1.cam.ac.uk server ntp2.cam.ac.uk peer beta.dept.cam.ac.uk peer gamma.dept.cam.ac.uk
driftfile /etc/ntp.drift server ntp0.cam.ac.uk server ntp1.cam.ac.uk server ntp3.cam.ac.uk peer alpha.dept.cam.ac.uk peer gamma.dept.cam.ac.uk
driftfile /etc/ntp.drift server ntp0.cam.ac.uk server ntp2.cam.ac.uk server ntp3.cam.ac.uk peer alpha.dept.cam.ac.uk peer beta.dept.cam.ac.uk
It is perfectly possible to set up peering arrangements between stratum 3 servers in different institutions, and in the case of networks with single servers it is advisable. To do this you need to find another department's or college's server whose manager is agreeable. It is sensible to select the other server to be one whose choice of stratum 2 servers is different from yours. Then you add the remote system as a peer and the remote system's administrator adds yours.
This can be done with the multiple server institution too. In this case it makes sense for each of the servers in one institution to select different peers, quite possibly from different remote institutions.