NTP Server Check
An NTP test sends a UDP NTP request to the specified server on port 123, reads the server's current timestamp, and calculates the clock offset relative to the probe node's local clock.
How to Use
• Server address：Enter the NTP server hostname or IP (e.g. pool.ntp.org, time.apple.com)
• What is checked：UDP port 123 connectivity, server timestamp read, clock offset calculation
• Offset meaning：Positive value means the server is ahead of local time; negative means behind
• Node selection：Optionally select specific nodes; all available nodes are used by default
What NTP server testing is for
An NTP test sends a UDP NTP request to the specified server on port 123, reads the server's current timestamp, and calculates the clock offset relative to the probe node's local clock. It confirms that the NTP server is reachable, responding to queries, and that its reported time is close to the reference.
Common uses include verifying that an NTP server is reachable before configuring it as a time source, diagnosing clock drift issues on servers by identifying large time offsets, confirming that a pool.ntp.org address resolves and responds correctly, and checking connectivity to an internal NTP server from an external probe.
Frequently asked questions
What is a normal clock offset?
Interpret NTP offset relative to the probe’s local clock, network delay and application needs. There is no universal passing threshold, and one request cannot establish long-term synchronization accuracy.
What does a positive vs negative offset mean?
A positive offset means the NTP server's clock is ahead of the probe node's clock. A negative offset means it is behind. The absolute value of the offset is what matters for synchronization quality.
Why is the NTP server not responding?
No NTP response can result from UDP 123 filtering, an inactive service, source restrictions or a timeout. Check the actual security-group and firewall rules rather than assuming a universal provider default.
What are the recommended public NTP servers?
pool.ntp.org is the most widely used public NTP pool. Cloud providers offer their own NTP servers (time.cloudflare.com, time.apple.com, time.google.com). For low-latency synchronization, use a server in the same region.
References and result limitations
Online results reflect the queried source or probe state at that time. Record the target, time, nodes or data source, and parameters when citing them. A single result does not establish continuous availability everywhere.
These references explain protocol or format rules; they do not endorse results produced by this site.