firewalld.service is a firewall service daemon that provides a dynamic, customizable firewall with a D-Bus interface. firewalld.service must be active to enforce rules configured through FirewallD. firewalld.service must be enabled to start automatically after a system reboot.
Solution
Run the following commands to unmask, enable, and start firewalld.service : # systemctl unmask firewalld.service # systemctl --now enable firewalld.service