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Details of the Network Time Protocol service

The Network Time Protocol (NTP) is the mechanism widely used on the Internet to distribute accurate time information which can then be used by systems on the Internet to set their clocks. A primary NTP server has a directly attached accurate time piece such as a radio clock or an atomic clock. A secondary NTP is one that is synchronised from other NTP servers.

The UIS runs a number of secondary NTP servers. These are synchronised from various primary servers including those run by Jisc (as part of their Network time service), the National Physical Laboratory (as part of their Internet Time Service) and the Department of Computer Science and Technology.

The University has four NTP servers for general access, three run by the UIS and one by the Department of Engineering. They are accessible under the DNS names, ntp0.cam.ac.uk, ntp1.cam.ac.uk, ntp2.cam.ac.uk, and ntp3.cam.ac.uk. All are accessible over IPv4, and all but ntp2 over IPv6 as well. The four servers are geographically diverse, so loss of a single server room should affect only a subset of them. This also ensures that they are in different thermal environments, which should avoid systematic timing errors.

Institutions may also wish to set up their own NTP servers for internal use.

The NTP Home Page
This is the main home page for NTP on the Internet, maintained partly by Dave Mills, the creator of the protocol.
Setting up an institutional server
This page covers the servers to use to set up one or more institutional servers.
Setting up a client
This page describes what servers to use if there is no institutional service local to your machine.

Please address queries about NTP within the University to timelord@uis.cam.ac.uk.

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If you have any enquiries regarding UIS network services, or other University network topics, please send an email to:

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