16.15. Configure the Firewall to Allow Incoming NTP Packets

The NTP traffic consists of UDP packets on port 123 and needs to be permitted through network and host-based firewalls in order for NTP to function.
Check if the firewall is configured to allow incoming NTP traffic for clients using the graphical Firewall Configuration tool.
To start the graphical firewall-config tool, press the Super key to enter the Activities Overview, type firewall and then press Enter. The Firewall Configuration window opens. You will be prompted for your user password.
To start the graphical firewall configuration tool using the command line, enter the following command as root user:
~]# firewall-config
The Firewall Configuration window opens. Note, this command can be run as normal user but you will then be prompted for the root password from time to time.
Look for the word Connected in the lower left corner. This indicates that the firewall-config tool is connected to the user space daemon, firewalld.

16.15.1. Change the Firewall Settings

To immediately change the current firewall settings, ensure the drop-down selection menu labeled Configuration is set to Runtime. Alternatively, to edit the settings to be applied at the next system start, or firewall reload, select Permanent from the drop-down list.

Note

When making changes to the firewall settings in Runtime mode, your selection takes immediate effect when you set or clear the check box associated with the service. You should keep this in mind when working on a system that may be in use by other users.
When making changes to the firewall settings in Permanent mode, your selection will only take effect when you reload the firewall or the system restarts. To reload the firewall, select the Options menu and select Reload Firewall.

16.15.2. Open Ports in the Firewall for NTP Packets

To permit traffic through the firewall to a certain port, start the firewall-config tool and select the network zone whose settings you want to change. Select the Ports tab and then click the Add button. The Port and Protocol window opens.
Enter the port number 123 and select udp from the drop-down list.