NIST Internet Time Servers

Return to NIST Internet Time Service Page

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. If you have difficulty using the name of a system, you can access a server using the IP address directly.

Important notes:

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.

3. The generic name time.nist.gov 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: jlevine@nist.gov

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.

Name IP Address Location Status
time-a.nist.gov 129.6.15.28 NIST, Gaithersburg, Maryland all services ok
time-b.nist.gov 129.6.15.29 NIST, Gaithersburg, Maryland All services ok
time-c.nist.gov 129.6.15.30 NIST, Gaithersburg, Maryland All services available
time-d.nist.gov 129.6.15.27 NIST, Gaithersburg, Maryland All services available
time-d.nist.gov 2610:20:6F15:15::27 NIST, Gaithersburg, Maryland All services via IPV6
time.maconbibb.us 98.175.203.200 Macon, Georgia name changed
wolfnisttime.com 66.199.22.67 Wolf-Tek, Birmingham, Alabama all services ok
nist.netservicesgroup.com 64.113.32.5 Southfield, Michigan All services available
nisttime.carsoncity.k12.mi.us 198.111.152.100 Carson City, Michigan Final shutdown coming
nist1-lnk.binary.net 216.229.0.179 Lincoln, Nebraska All services available
wwv.nist.gov 24.56.178.140 WWV, Fort Collins, Colorado All services available
time-b-wwv.nist.gov 132.163.97.2 WWV, Fort Collins, Colorado All services avaiable
time-c-wwv.nist.gov 132.163.97.3 WWV, Fort Collins, Colorado All services available
time-d-wwv.nist.gov 132.163.97.4 WWV, Fort Collins, Colorado All services available
time-d-wwv.nist.gov 2610:20:6f97:97::4 WWV, Fort Collins, Colorado All Services via IPv6
time-a.timefreq.bldrdoc.gov 132.163.4.101 NIST, Boulder, Colorado Address change coming
time-b-b.nist.gov 132.163.96.2 NIST, Boulder, Colorado All services avaialble
time-c-b.nist.gov 132.163.96.3 NIST, Boulder, Colorado All services available
time-d-b.nist.gov 132.163.96.4 NIST, Boulder, Colorado All services available
time-d-b.nist.gov 2610:20:6f96:96::4 NIST, Boulder, Colorado Services via IPv6
time.nist.gov global address for all servers Multiple locations All services available
utcnist.colorado.edu 128.138.140.44 University of Colorado, Boulder All services available
utcnist2.colorado.edu 128.138.141.172 University of Colorado, Boulder All services available
nist-time-server.eoni.com 216.228.192.69 La Grande, Oregon All services available
nist-time-server.eoni.com 2607:f248::45 La Grande, Oregon All services also via ipv6

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.

Name IP Address Location Status
ntp-a.boulder.nist.gov 132.163.4.107 NIST, Boulder, Colorado Planned shutdown, 11/1
ntp-b(b).nist.gov 132.163.96.5 NIST, Boulder, Colorado Available, 11/1
ntp-b.nist.gov 24.56.178.141 NIST WWV, Fort Collins, Colorado Planned shutdown, 11/1
ntp-wwv.nist.gov 132.163.97.5 NIST WWV, Fort Collins, Colorado Authenticated service
ntp-c.colorado.edu 128.138.141.177 JILA, Univ. of Colorado, Boulder Authenticated Service
ntp-d.nist.gov 129.6.15.32 NIST, Gaithersburg, Maryland Authenticated Service

The following server supports only the NTP format and transmits UT1 time rather than UTC(NIST). For details about the UT1 server, please see the UT1 NTP Information page.
ut1-time.colorado.edu 128.138.140.50 University of Colorado, Boulder