NTP clients not receiving updates

Symptoms

• Clients are not receiving NTP responses from the server
• Clients were previously synchronized, but have stopped receiving NTP updates
• Clients drift out of sync or report the NTP server as unreachable

Causes

• Network configuration prevents NTP traffic from reaching clients
• Clients are referencing an outdated or incorrect IP address for the NTP server. If the GMR is configured for DHCP, a DHCP server may assign a new IP address after a reboot or network change.
• Firewall rules are blocking NTP traffic (UDP port 123)
• NTP service is not running or has stopped unexpectedly
• The server is not synchronized to its reference source (for example, GPS lock is not achieved)

Troubleshooting steps

1. Confirm the NTP service is running on the GMR.
   If the service is stopped, clients will not receive time updates.
2. Verify the GMR is synchronized to a valid reference source.
   Check device status to confirm it is locked to GPS or another configured reference.
3. Check network connectivity between clients and the GMR.
   Confirm clients can reach the GMR over the network using tools such as ping or traceroute. These checks do not establish that UDP port 123 traffic is permitted.
4. Verify firewall and security rules allow NTP traffic.
   Ensure UDP port 123 is permitted between the GMR and all NTP clients.
5. Confirm clients reference the GMR’s current IP address.
   Verify the configured server address matches the GMR’s current IP (especially if DHCP is enabled).

Related articles

Time Dissemination During Reference Outages

• Clients cannot sync to the NTP server
• NTP stops serving time when reference is lost