Accurate time synchronisation across computer networks is important for time-stamping in security systems, reliable log-scanning to analyse security breaches, and the maintenance of consistency in distributed file systems.

NTP is designed to be highly fault-tolerant. For this purpose it is usually best for a machine to be connected to several different servers with independent paths back to a primary time source. It is also usual for machines to "peer" with others at the same stratum to increase overall resillience of the protocol.

OUCS run four stratum-2 time servers available to any IPv4 host:

server  ntp0.ox.ac.uk            # OUCS stratum-2 server
server  ntp1.ox.ac.uk            # OUCS stratum-2 server
server  ntp2.ox.ac.uk            # OUCS stratum-2 server
server  ntp3.ox.ac.uk            # OUCS stratum-2 server

A DNS round robin of ntp.ox.ac.uk exists for the above

OUCS run four stratum-3 time servers available to any IPv4 host

Historically these were used by clients where no unit NTP server existed. Many hosts currently use these and there's no plan to decommission these at this time. There will be no significant time difference with the stratum 2:

server  ntp0.oucs.ox.ac.uk            # OUCS stratum-3 server
server  ntp1.oucs.ox.ac.uk            # OUCS stratum-3 server
server  ntp2.oucs.ox.ac.uk            # OUCS stratum-3 server
server  ntp3.oucs.ox.ac.uk            # OUCS stratum-3 server

A DNS round robin of ntp.oucs.ox.ac.uk exists for the above

NTP is defined in RFC 1305, Network Time Protocol (version 3)

Your /etc/ntp.conf file should look something like this.

server  ntp0.ox.ac.uk            # OUCS stratum-2 server
server  ntp1.ox.ac.uk            # OUCS stratum-2 server
server  ntp2.ox.ac.uk            # OUCS stratum-2 server
server  ntp3.ox.ac.uk            # OUCS stratum-2 server
peer    ntp0.yourunit.ox.ac.uk   # (optionally) peered with 
peer    ntp1.yourunit.ox.ac.uk   # stratum-3 departmental servers

Please note that the IP addresess of NTP servers may occasionally be subject to change, although OUCS will endeavour to minimise the frequency of such changes. Notice will be given to the itss-announce mailing list.