Return to NIST Internet Time Service Page
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The following table lists time servers for the NIST Internet Time Service (ITS), organized geographically from North to South and East to West within the US. While server names are generally accurate, NIST only controls nist.gov server names. For connection issues with server names, use the direct IP address.
Important Notes:
- The “TIME” protocol (tcp port 37) is supported but discouraged due to bandwidth inefficiency. Users are strongly advised to upgrade to Network Time Protocol (NTP) for better accuracy and robustness.
- Users of the NIST “DAYTIME” protocol (tcp port 13) should also upgrade to NTP for improved accuracy and lower bandwidth usage. The NIST time client (nistime-32bit.exe) supports both protocols.
- The generic name time.nist.gov will continue to resolve to all servers via round-robin DNS for load balancing. Using this name is recommended.
For comments, please contact: [email protected]
The global address time.nist.gov resolves to all listed server addresses in a round-robin sequence to distribute load evenly.
Avoid hardcoding specific server names or IP addresses into devices to allow for future flexibility and changes.
Ensure your software NEVER queries a server more than once every 4 seconds to prevent service refusal or being flagged as a denial-of-service attempt.
| 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-f-wwv.nist.gov | 132.163.97.8 | WWV, Fort Collins, Colorado | Only NTP service |
| 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 | All services available |
The following servers exclusively support authenticated NTP requests using symmetric key encryption as detailed in NTP documentation. They do not respond to DAYTIME or TIME format requests and reject anonymous ftp connections. Registration with NIST is required to obtain an encryption key for these systems. Unregistered users’ NTP requests will be denied. Refer to the authenticated NTP description for further details.
| 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 server below supports only NTP and transmits UT1 time instead of UTC(NIST). See the UT1 NTP Information page for UT1 server specifics.
| 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 |
