Clients cannot sync to the NTP server

Symptoms

• NTP clients do not synchronize to the server
• Clients report no response or unsynchronized status
• NTP synchronization worked previously and has stopped

Causes

• Client configuration or reachability issues
• Compatibility settings affecting packet acceptance
• Upstream reference unavailable or unstable

Troubleshooting steps

1. Verify the current server IP address and basic reachability from the affected client.
2. Confirm UDP port 123 is permitted between client and server. Ping alone does not verify NTP traffic.
3. Confirm standard client mode. Some Masterclock devices do not support authentication or symmetric active modes; check the documentation for the model in use.
4. Check Output Control and reference status. Confirm the device is configured to serve NTP and is not reporting an alarm state that causes the client to reject it.

Related articles

Time Dissemination During Reference Outages

• NTP clients not receiving updates
• Why NTP stratum 16 indicates unsynchronized state