The global address time.nist.gov is resolved to all of the server addresses below in a round-robin sequence to equalize the load across all of the servers.

Whether you connect to a server using the name or the IP address, it is a bad practice to “hard-code” a particular server name or address into a device so that these parameters cannot be changed by the end user if that becomes necessary at some future time.

All users should ensure that their software NEVER queries a server more frequently than once every 4 seconds. Systems that exceed this rate will be refused service. In extreme cases, systems that exceed this limit may be considered as attempting a denial-of-service attack.

The following servers support only authenticated NTP requests using the symmetric key encryption method that is defined in the NTP documentation. They do not respond to requests for time in the DAYTIME or TIME formats and will not accept anonymous ftp connections. You must apply to NIST for an encryption key to use these systems; they will not respond to NTP requests from users who have not registered with NIST.
See the authenticated NTP description for more information.

Because requests for NIST Internet Time Service continue to rapidly grow, we are always interested in the possibility of expanding the number of servers and broadening their geographic distribution. All organizations interested in possibly hosting a NIST Internet Time Service server are invited to contact Judah Levine for more information, including a description of the equipment that the organization must have available and a discussion of the other technical qualifications necessary to host a server: jlevine@nist.gov . NIST does not charge the hosting organization for this service.