- NIST confirmed that several public time servers lost their atomic reference signal
- A generator failure disrupted the distribution of the United States primary atomic time scale.
- Some NIST servers responded normally while silently delivering inaccurate timestamps
The National Institute of Standards and Technology (NIST) has issued an alert that some of its public time servers may be unreliable.
The advisory focuses on a defined set of hosts, including multiple time-xb.nist.gov addresses and the ntp-b.nist.gov authenticated service.
According to NIST, these systems can still respond to network requests without referencing a valid atomic time source.
What went wrong at the Boulder facility
To prevent the spread of incorrect data, the agency said it may temporarily take some of the affected hosts offline.
NIST traced the problem to its Boulder, Colorado, campus, where an extended power outage disrupted operations.
The outage occurred during high winds that damaged power lines and led to safety-related shutdowns.
Although backup power systems existed, a generator failure interrupted the atomic time scale distribution that powers the Internet Time Service.
NIST stated that the UTC(NIST) signal drifted approximately four microseconds during the incident, a deviation that is small but measurable.
The outage does not affect all NIST timing endpoints. Widely used addresses, such as time.nist.gov, are based on round robin DNS and a geographically distributed infrastructure.
This design allows clients to automatically fall back to unaffected locations when a site encounters problems.
Users who hardcode individual hostnames face greater exposure to localized failures like this.
Systems running on cloud hosting platforms often rely on pooled or upstream timing sources, which can hide short-lived issues within a single installation.
The Boulder site is home to the NIST-F4 atomic clock, which uses cesium atoms to define the length of a second with extreme precision, underpinning services used by telecommunications networks, power grids, financial platforms, and scientific research.
Precise synchronization is also critical for data center hosting environments, where synchronization impacts logging, security protocols, and transaction order in distributed systems.
Many enterprise servers rely on external authoritative sources, making upstream accuracy a shared dependency.
This incident follows another time service outage earlier this month at the NIST facility in Gaithersburg, Maryland, which caused a larger time step error measured in milliseconds, not microseconds.
NIST has not given a firm timeline for full restoration in Boulder and said engineers are continuing recovery work.
While most consumer systems are unlikely to notice the issue, high precision users are expected to monitor multiple independent references.
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