Firewalld

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firewalld is a firewall daemon developed by Red Hat. It uses nftables by default. From project home page:

Firewalld provides a dynamically managed firewall with support for network/firewall zones that define the trust level of network connections or interfaces. It has support for IPv4, IPv6 firewall settings, ethernet bridges and IP sets. There is a separation of runtime and permanent configuration options. It also provides an interface for services or applications to add firewall rules directly.

Installation

Install the firewalld package.

Usage

Enable and start firewalld.service.

You can control the firewall rules with the firewall-cmd console utility.

firewall-offline-cmd utility can be used to configure when firewalld is not running. It features similar syntax to firewall-cmd.

GUI is available as firewall-config which comes with firewalld package.

Configuration

Configuration at run time can be changed using firewall-cmd.

Note: Most commands will only change runtime configuration and will not persist through restart. To make changes permanent there are two options:

Use --permanent option. This will not change runtime configuration until the firewall service is restarted or rules are reloaded with --reload command.
Change the runtime configuration and make it permanent as described in #Converting runtime configuration to permanent

Zones

Zone is a collection of rules that can be applied to a specific interface.

To have an overview of the current zones and interfaces they are applied to:

# firewall-cmd --get-active-zones

Some commands (such as adding/removing ports/services) require a zone to specified.

Zone can be specified by name by passing --zone=zone_name parameter.

If no zone is specified default zone is assumed.

Zone information

You can list all the zones with entirety their configuration:

# firewall-cmd --list-all-zones

or just a specific zone

# firewall-cmd --info-zone=zone_name

Changing zone of an interface

# firewall-cmd --zone=zone --change-interface=interface_name

There zone is a new zone that you want to assign interface to.

Using NetworkManager to manage zones

NetworkManager can assign different connection profiles to different zones. This allows for example, adding a home WiFi connection to the "home" zone, a work WiFi connection to the "work" zone, and all other WiFi connections to the default "public" zone.

List connection profiles:

$ nmcli connection show

Assign the "myssid" profile to the "home" zone:

$ nmcli connection modify myssid connection.zone home

Default zones

When a new interface is connected the default zone will be applied. You can query the name of the default zone using:

# firewall-cmd --get-default-zone

The default zone can be changed using following command.

# firewall-cmd --set-default-zone=zone

Note: This change is always permanent.

Services

Services are pre-made rules corresponding to a specific daemon. For example, the ssh service corresponds to SSH and opens ports 22 when assigned to a zone.

To get a list of available services, enter the following command:

# firewall-cmd --get-services

You can query information about a particular service:

# firewall-cmd --info-service service_name

Adding or removing services from a zone

To add a service to a zone:

# firewall-cmd --zone=zone_name --add-service service_name

Removing a service:

# firewall-cmd --zone=zone_name --remove-service service_name

Ports

Ports can be directly opened on a specific zone.

# firewall-cmd --zone=zone_name --add-port port_num/protocol

There protocol is either tcp or udp.

To close the port use --remove-port option with same port number and protocol.

NAT masquerade

This command has the same effect as iptables -t nat -A POSTROUTING -j MASQUERADE:

# firewall-cmd --zone=public --add-masquerade

Port forwarding

If you have firewalld configured on a router, and you have enabled NAT masquerading as above, it is simple to set up port forwarding through firewalld:

# firewall-cmd --zone=public --add-forward-port=port=12345:proto=tcp:toport=22:toaddr=10.20.30.40

This will forward port 12345/tcp on the firewall's public interface to port 22 (standard SSH) on the internal system at IP address 10.20.30.40. To remove this forwarded port:

# firewall-cmd --zone=public --remove-forward-port=port=12345:proto=tcp:toport=22:toaddr=10.20.30.40

Unfortunately you have to type the entire forward declaration in order to remove it, specifying only the port and the protocol is not enough.

Tips and tricks

Port or service timeout

Service or port can be added for a limited amount of time using --timeout=value option passed during addition command. Value is either number of seconds, minutes if postfixed with m or hours h. For example, adding SSH service for 3 hours:

# firewall-cmd --add-service ssh --timeout=3h

Note: Timeouts are mutually exclusive with --permanent changes to the firewall configuration. I.e., timeouts can only be applied to the runtime configuration, and are never permanent.

Converting runtime configuration to permanent

You can make the runtime (current temporary) configuration permanent (meaning it persists through restarts)

# firewall-cmd --runtime-to-permanent

Check services details

The configuration files for the default supported services are located at /usr/lib/firewalld/services/ and user-created service files would be in /etc/firewalld/services/.