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Some local networks within the University have their own NTP servers, so if your local IT staff provide recommendations for NTP configuration, follow those. Otherwise, read on.

Full NTP clients

If your NTP client software allows you to configure multiple servers, you should use some or (preferably) all of:

  • ntp0.cam.ac.uk
  • ntp1.cam.ac.uk
  • ntp2.cam.ac.uk
  • ntp3.cam.ac.uk

If you can't configure all of them, prefer the ones with lower numbers.

If using the Official Reference Implementation of NTP, or chrony, a configuration like this is recommended:

server ntp0.cam.ac.uk iburst
server ntp1.cam.ac.uk iburst
server ntp2.cam.ac.uk iburst
server ntp3.cam.ac.uk iburst

Simple NTP (SNTP) clients

Simple NTP (SNTP) clients can only handle a single server. These should be configured to use sntp.cam.ac.uk. While each of ntp0, ntp1, etc refers to a single physical server, sntp is a virtual address that is automatically moved between servers so that it's (almost) always available.

IP addresses

Some clients can't handle DNS names, or need to work when DNS isn't available. You can use the IP addresses (IPv4 or IPv6) corresponding to the names above. Be aware, though, that they might change. We intend to keep any withdrawn address working for at least a year after it's removed from the DNS, so if you update the addresses once a year you should be fine.

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