Firewalld is the default firewall software for CentOS 7/8, Fedora, and other Linux distributions based on Red Hat. This quick start guide lists some common commands for Firewalld, enabling system administrators to rapidly master its usage.

Checking if Firewalld is Running:

$ firewall-cmd --state
running

Retrieve Active Zones:

$ firewall-cmd --get-active-zones
public
    interfaces: ens3

List Running Ports and Services (for the 'public' zone):

$ firewall-cmd --zone=public --list-ports
7000-8000/tcp

$ firewall-cmd --zone=public --list-services
cockpit dhcpv6-client ssh

Enabling SSH Access (choose one of the following two methods):

$ firewall-cmd --add-service=ssh --permanent
$ firewall-cmd --add-port=22/tcp --permanent
$ firewall-cmd --reload

Permanent and Temporary Modes:

The permanent mode requires the addition of the --permanent option when executing commands, and the changes will take effect only after running firewall-cmd --reload or restarting the server. The temporary mode does not require any additional options during command execution and takes effect immediately. However, the settings will be lost after a server reboot. For instance, to permanently allow SSH access, execute the following command.

$ firewall-cmd --zone=public --add-service=ssh --permanent
$ firewall-cmd --reload

Disabling and Stopping Firewalld:

# systemctl stop firewalld.service
# systemctl disable firewalld.service

For more information, refer to the official Firewalld documentation.

https://firewalld.org/documentation/