Cisco router or switch fails to synchronize time

In rare cases, time synchronization (NTP) fails even when logging into a Cisco device and pinging an NTP server. In such cases, specifying the interface to be used for time synchronization with the NTP server may work.
For example, as shown in the figure below, you may want to look at the NTP server over the WAN.
If the time synchronization is not working, the log time will be inconsistent and failure investigations may not be successful, so it is necessary to resolve the error.

Translated with www.DeepL.com/Translator (free version)

Execute the following commands on the router at base B.

router (config)# ntp source VLAN "VLAN number on WAN side"
Or, use the following command
router (config)# ntp source interface GigabitEthernet "Interface (1/0/1) connected to the WAN."

After setting, confirm that time synchronization has been successfully performed by using the following command.
It may take more than 5 minutes depending on the range of time discrepancy.

router#show ntp status

If the status of “Clock is synchronizaed, ~” comes back, it is done.

for your reference.