Public NTP Time Servers

From NBS Special Publication 432 (out of print)

These pages contain lists of Network Time Protocol (NTP) public time servers. They are provided for information purposes only and represents the best information available at the current date. It does not represent a commitment to provide connectivity or time service on the part of the operators involved. Further information of a technical nature can be obtained from the ntp at ni.umd.edu list. To subscribe to this list, contact ntp-request at transsys.com - Louie Mamakos <ntp-request at ntp.transsys.com Alternatively, if possible, please subscribe to the newsgroup comp.protocols.time.ntp which is gatewayed to the mailing list.

Rules of Engagement

As the load on the hosts supporting NTP primary (stratum 1) time service is heavy and always increasing, clients should avoid using the primary servers whenever possible. In most cases the accuracy of the NTP secondary (stratum 2) servers is only slightly degraded relative to the primary servers and, as a group, the secondary servers may be just as reliable. As a general rule, a secondary server should use a primary server only under the following conditions:

The secondary server provides synchronization to a sizable population of other servers and clients on the order of 100 or more.
The server operates with at least two and preferably three other secondary servers in a common synchronization subnet designed to provide reliable service, even if some servers or the lines connecting them fail.
The administration(s) that operates these servers coordinates other servers within the region, in order to reduce the resources required outside that region. Note that at least some interregional resources are required in order to ensure reliable service.

In order to ensure reliability, clients should spread their use over many different servers. As a general rule, no more than two clients per network should use the same server on another network; however, in order to simplify management of host configuration tables, many hosts on the same network may use the same (redundant) servers on the same network.

Unix users are strongly encouraged to adopt the latest NTP version software in the compressed tar distribution shown in the NTP home page. Besides providing more accurate, reliable service, the latest version automatically increases the polling intervals for all peer associations, but without sacrificing performance. This can significantly reduce network loads, as well as the loads on the busy primary servers, some of which have over 700 clients.

Public NTP Time Servers

The list of primary (stratum 1) and secondary (stratum 2) designates the NTP time servers available for public access under stated restrictions. Each entry gives the host name, Internet address, approximate location and geographic coordinates (if available), synchronization source (stratum, type of radio or satellite receiver and host type), suggested service area, access policy (as notified) and responsible person name and e-mail address. Most servers indicate the NTP version as well. It is always wise to consult the DNS to verify host addresses, which are changed from time to time. When more than one address is given, preference should given to each in order. All servers are equipped with uncompensated crystal-stabilized timebases, unless indicated otherwise.

It is very important that potential clients avoid use of servers not listed as open access, unless approved first by the responsible person. This especially includes indiscriminate use of servers not listed in the list, since this can be disruptive. The responsible person should always be notified upon establishment of regular operations with servers listed as open access. Please respect the access policy as stated by the responsible person. Servers listed as closed access should NOT be used without prior permission, since this may disrupt ongoing activities in which these servers are involved.