OIT Network Switching and Routing

Retirement of Legacy Network Time Protocol (NTP) Servers

OIT Networking & Monitoring Services
May 13 2019
Last Updated: 2:27 pm May 13 2019

Network Time Protocol (NTP) Service allows a device to learn the date and time and to keep its clock synchronized to an accurate time source.

The servers OIT operates to provide this service to most of the wired Campus Data Network (CDN) are legacy equipment. During 2018-2019, OIT installed new servers to continue providing this service. The legacy servers which have provided the service will be retired on August 6 2019 as announced by OIT.

Some devices which used the legacy NTP servers retired have already automatically switched to using the new NTP servers, so will not be affected by the retirement of the legacy NTP servers. Some devices are still using the legacy NTP servers; action may be needed to switch those devices to use the new NTP servers before the legacy NTP servers are retired.

Potentially affected devices fall into several categories:

Devices connected via wireless services provided by OIT:
These devices are supposed to use DHCP to obtain their IP configuration. That DHCP service tells these devices which NTP servers they should use, among other things.

These devices will not be affected by the retirement of the legacy NTP servers. (The NTP servers supporting wireless services provided by OIT are not the legacy NTP servers.)

Devices connected via network wingnet:
These devices are supposed to use DHCP to obtain IP configuration. That DHCP service tells these devices which NTP servers they should use, among other things.

These devices will not be affected by the retirement of the legacy NTP servers. (The NTP servers supporting network wingnet are not the legacy NTP servers.)

Devices attached to Princeton Private Network (PPN) Networks:
As OIT provides no NTP service to these networks, devices attached to these networks are not affected by this change.

Devices attached to OIT VoIP Networks:
Devices attached to these networks are not affected by this change. OIT provides NTP service on these networks with a different set of NTP servers, not the ones being replaced in this change.

Devices attached to other Campus Data Network (CDN) where OIT does not provide NTP service:
As OIT provides no NTP service to these networks, devices attached to these networks are not affected by this change.

Devices attached to other Campus Data Network (CDN) where OIT provides NTP service:
These devices might be using different ways to obtain their IP configuration:

If the device obtains its IP configuration via DHCP service provided by OIT:
Restart the device on or after May 8 2019. Once it restarts, the DHCP client software will learn of the new NTP servers.

If the device obtains its IP configuration via BootP service provided by OIT, or via manual configuration:
BootP service provided by OIT does not (intentionally) provide a list of NTP servers to clients, so for this purpose, may be treated the same as manually-configured devices.

Unless your device was manually configured your device to use NTP service provided by OIT, your device is not using NTP service provided by OIT. Your device will be unaffected by the replacement of NTP servers; no action is needed.

If your device was manually configured to use NTP service provided by OIT, verify it was configured to use the NTP servers (DNS names) documented Network Time Protocol (NTP) Service. Be sure you have specified the NTP servers names, not their IP addresses. Restart the device on or after May 8 2019. Once it restarts, the NTP client software will use the new NTP servers.

If the device obtains its IP configuration via DHCP service or BootP service provided by someone other than OIT:
See All others cases below.

All other cases
If your device obtains DHCP or BootP service from a service other than OIT's, you'll need to check with the group that operates that DHCP or BootP service to learn if that service directs your device to use NTP service provided by OIT, and if so, whether you need to take action.

If your device was manually configured to use NTP service provided by OIT, verify it was configured to use the NTP servers (DNS names) documented in Network Time Protocol (NTP) Service. Be sure you have specified the NTP servers names, not their IP addresses. Restart the device on or after May 2 2019. Once it restarts, the NTP client software will use the new NTP servers.


Technical Information

We provide this additional technical information for those customers who need it; most will not need this level of detail.

The legacy NTP servers operated by OIT for most of the wired portions of the Campus Data Network (CDN) were named ntp1.princeton.edu, ntp2.princeton.edu, ntp3.princeton.edu, and ntp4.princeton.edu. (These are DNS CNAMES, that is, host aliases.)

The new NTP servers providing that service have the same names as the old servers; the names have moved to the new servers. (As there were four legacy NTP servers, but only three new NTP servers, the names ntp3.princeton.edu and ntp4.princeton.edu both point to the same new server.)

While the DNS names of these NTP servers have not changed, the IP addresses of the new NTP servers are different than the IP addresses of the legacy NTP servers. The DNS names above were updated on May 1 2019 so they resolve to the new NTP servers' IP addresses instead of the legacy NTP servers' IP addresses.

OIT is running both the legacy and new NTP servers in parallel until August 6 2019. On that day, OIT will retire NTP service on the legacy NTP servers.

Clients configured to the NTP servers' DNS names need no reconfiguration; the DNS names continue to be valid, and resolve to the new NTP servers' IP addresses. But if the NTP client software started prior to May 2 2019, it may still be using the legacy NTP servers' IP addresses; it should be restarted to ensure it switches to use the new NTP servers. The simplest way to restart the NTP client software is to reboot the client device. (For some operating systems it may be possible to restart just the NTP client software to avoid needing to restart the device; if you wish to pursue this course, you will need to consult your operating systems' documentation to learn if it is feasible for your operating system.)

When DHCP provided by OIT provides a list of NTP servers to a DHCP client, it provides a list of IP addresses, not a list of DNS names. On those networks where those DHCP servers provided to DHCP clients a list of the legacy NTP servers' IP addresses, those DHCP servers were updated by OIT during Spring 2019 (completed on May 7 2019) to instead provide the list of new NTP servers' IP addresses. If the DHCP client (re)started on or after May 8 2019, the DHCP service provided to the client the new NTP servers' IP addresses, so no action is needed. If the DHCP client last started prior to May 8 2019, it should be restarted so it learns the new NTP server IP addresses.

Some DHCP clients ignore any list of NTP servers provided by DHCP service, and instead use some other NTP server list built-into the operating system, or a manually configured list of NTP servers, or synchronize their clocks via other mechanisms.


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