Firewalld is the default software firewall for Fedora, CentOS 7, and other modern distributions based on Red Hat or SUSE Linux. This quickstart guide outlines several useful commands and techniques to assist debugging Firewalld.
$ firewall-cmd --state
running
$ firewall-cmd --get-active-zones
public
interfaces: ens3
Assuming your active zone is public, this quick check reveals what traffic is allowed.
$ firewall-cmd --zone=public --list-ports
7000-8000/tcp
$ firewall-cmd --zone=public --list-services
cockpit dhcpv6-client ssh
Assuming your active zone is public, use either of these two methods to allow SSH.
$ firewall-cmd --zone=public --add-service=ssh
or
# firewall-cmd --add-port=22/tcp
As root, use the --panic-on switch.
# firewall-cmd --panic-on
All packets will be dropped. Active connections will be terminated after a period of inactivity.
As root, use the --panic-off switch.
# firewall-cmd --panic-off
firewall-cmd --query-panic && echo "enabled" || echo "Not enabled"
Temporary changes cause a common issue; the server works as expected until the next reboot. Make sure you permanently save your configuration.
To make a command permanent, add the --permanent option to all commands except --direct commands (which are temporary by nature). Setting made with the --permanent option do not take effect until the next firewall reload, service restart, or system reboot. Settings made without the --permanent option take effect immediately, but are only valid until the next firewall reload, system boot, or service restart.
As root, mask and disable the service.
# systemctl mask --now firewalld.service
# systemctl disable --now firewalld.service