Primary and secondary time server information

The basic source of information on the location of stratum 1 and good quality stratum 2 servers is the World Wide Web page at the URL: http://www.eecis.udel.edu/~ntp. This contains up-to-date information on time servers.

Since there is an increasingly heavy load on the hosts supporting NTP, avoid using primary (stratum 1) servers. Secondary (stratum 2) servers are close in accuracy to stratum 1 servers. As a group, they may be just as reliable.

As a general rule, you should only use primary (stratum 1) servers under the following conditions:

• The server provides synchronization to a group of 100 or more clients.

• The server operates with at least two (preferably three) other local servers in a common synchronization subnet designed to provide reliable service.

• The administration that operates the subnet coordinates other clients within the region to reduce resources required outside the region. At least some interregional resources are required to ensure reliable service.