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.