NIST Internet Time Servers

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The table below lists the time servers used by the NIST Internet Time Service (ITS). The table lists each server's name, IP address, and location, organized geographically within the US from North to South and then from East to West. Please note that while we make every effort to ensure that the names of the servers are correct, we control the names of only the servers. If you have difficulty using the name of a system, you can access a server using the IP address directly.

28 February, 2013     Important changes:

1. We will continue to support the "TIME" protocol that uses tcp port 37 for the forseeable future. However, this protocol is very expensive in terms of network bandwidth, since it uses the complete tcp machinery to transmit only 32 bits of data. Users are *strongly* encouraged to upgrade to the network time protocol (NTP), which is both more accurate and more robust.

2. Users of the NIST "DAYTIME" protocol on tcp port 13 are also strongly encouraged to upgrade to the network time protocol, which provides greater accuracy and requires less network bandwidth. The NIST time client (nistime-32bit.exe) supports both protocols. We expect to replace the tcp version of this protocol with a udp-based version near the end of 2013.

3. The generic name will continue to point to all of our servers on a round-robin basis, and users are encouraged to access the service using this name.

Please address comments to:

The global address 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.

Name IP Address Location Status Hatfield, PA All services available NIST, Gaithersburg, Maryland All services busy, not recommended NIST, Gaithersburg, Maryland All services busy, not recommended NIST, Gaithersburg, Maryland All services available 2610:20:6F15:15::27 NIST, Gaithersburg, Maryland All services via IPV6 Macon, Georgia All services available Birmingham, Alabama All services available Carrollton, Texas All services available Monroe, Michigan temporary failure Southfield, Michigan All services available Carson City, Michigan All services available Lincoln, Nebraska All services available WWV, Fort Collins, Colorado All services available NIST, Boulder, Colorado ntp ok; time, daytime busy NIST, Boulder, Colorado All services busy NIST, Boulder, Colorado ntp ok; time, daytime busy global address for all servers Multiple locations All services available University of Colorado, Boulder All services available University of Colorado, Boulder All services available LDSBC, Salt Lake City, Utah All services available Las Vegas, Nevada All services available Microsoft, Redmond, Washington All services very busy La Grande, Oregon All services available

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. NIST, Boulder, Colorado NIST WWV, Fort Collins, Colorado

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: . NIST does not charge the hosting organization for this service.