NIST Internet Time Service

NIST Internet Time Servers

Return to NIST Internet Time Service Page

NOTICE: NIST has established a mailing list (Google Group) to inform users of status changes of the Internet Time Service.
If you wish to subscribe to this list, please send your name and email address to: [email protected]

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 nist.gov servers. 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: [email protected]

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-g.nist.gov

129.6.15.28

NIST, Gaithersburg, Maryland

All Services available

time-b-g.nist.gov

129.6.15.29

NIST, Gaithersburg, Maryland

All services available

time-c-g.nist.gov

129.6.15.30

NIST, Gaithersburg, Maryland

All services available

time-d-g.nist.gov

129.6.15.27

NIST, Gaithersburg, Maryland

All services available

time-d-g.nist.gov

2610:20:6f15:15::27

NIST, Gaithersburg, Maryland

All services available

time-e-g.nist.gov

129.6.15.26

NIST, Gaithersburg, Maryland

All services available

time-e-g.nist.gov

2610:20:6f15:15::26

NIST, Gaithersburg, Maryland

All services available

time-a-wwv.nist.gov

132.163.97.1

WWV, Fort Collins, Colorado

All services available

time-b-wwv.nist.gov

132.163.97.2

WWV, Fort Collins, Colorado

All services available

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-e-wwv.nist.gov

132.163.97.6

WWV, Fort Collins, Colorado

All services available

time-e-wwv.nist.gov

2610:20:6f97:97::6

WWV, Fort Collins, Colorado

new server, services via IPV6

time-a-b.nist.gov

132.163.96.1

NIST, Boulder, Colorado

All services available

time-b-b.nist.gov

132.163.96.2

NIST, Boulder, Colorado

All services available

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

All services available

time-e-b.nist.gov

132.163.96.6

NIST, Boulder Colorado

All services available

time-e-b.nist.gov

2610:20:6f96:96::6

NIST, Boulder, Colorado

All services available

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

utcnist3.colorado.edu

128.138.140.211

University of Colorado, Boulder

NTP only, Recommended

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-b.nist.gov

132.163.96.5

NIST, Boulder, Colorado

Authenticated service

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

ut1-wwv.nist.gov
132.163.97.7
NIST WWV Radio, Ft. Collins, CO