En/4.0/Time synchronization service (NTP)
Zentyal integrates ntpd (2) as its NTP server. NTP uses UDP port 123.
Configuring an NTP server with Zentyal
Zentyal uses the NTP server to both synchronise its own clock and offer this service on the network, it's generally recommended to install and enable this service in most deployments.
Once you have enabled the module, you can check in System ‣ General that it is running and that manually adjusting the time is disabled. You still need to configure your time zone.
If you access to NTP, you can enable or disable the service, and choose the external servers that you want to synchronize to. By default, the list has already three preconfigured servers, chosen from the NTP project (3).
Once Zentyal is synchronised, you can offer your clock timing using the NTP service, generally through DHCP. As always, you must not forget to check the firewall rules, as NTP is usually enabled only for internal networks.