(Portions adapted from an OIT KnowledgeBase page.)
Network Time Protocol (NTP) Service allows devices to set their date/time clock to a known-good clock, and to keep their clock synchronized with a high degree of accuracy.
CS provides several NTP servers for use by devices attached to the campus network.
At the time of this writing, the NTP service we provide supports version 4 of the Network Time Protocol, and provides backward-compatibility with version 1, version 2, and version 3.
Some TCP/IP clients can use DHCP to learn the current list of appropriate NTP servers. The DHCP service provided by OIT does include NTP servers in the information it provides.
Many TCP/IP clients cannot learn the current list of NTP servers via DHCP. (Some clients do not use DHCP. And although many do use DHCP, currently many ignore the list of NTP servers provided by DHCP.) In those cases, if you wish to use CS NTP Service, you must manually configure your TCP/IP client with a list of appropriate NTP servers. Here is a list of recommended NTP servers for everywhere on campus:
- ntp1.cs.princeton.edu
- ntp2.cs.princeton.edu
If possible, configure your NTP client to use all of the NTP servers listed above.
There may be times when fewer than all three of these NTP servers are up. We periodically take down the servers (usually one at a time) for maintenance without any public announcement. We rely on the fact that a robust NTP client should be configured to synchronize to multiple NTP servers. (If your NTP client may only be configured with a single NTP server, select any one of the above; no one of the three is better than the others. Note your client will lose NTP service whenever the specified NTP server is down.)
When configuring your NTP client, be sure to specify NTP servers using the hostnames above, and not by IP address. The IP addresses associated with these hostnames may change without notice.