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CompTIA Linux+ XK0-005 - 2.3 - Common Firewall Technologies: firewalld

Firewalls are critical components of a secure computer system or network, controlling and filtering network traffic. In the context of the CompTIA Linux+ exam, understanding how to implement and configure firewalls is essential for maintaining a secure Linux environment. One common firewall technology used in Linux distributions is firewalld. This guide will provide you with a step-by-step approach to configuring firewalld.

Common Firewall Technology: firewalld

firewalld is a dynamic firewall management tool used in many Linux distributions, including Fedora, CentOS, and RHEL. It provides a user-friendly command-line interface and a D-Bus interface for easy configuration and management of firewall rules. Here's how you can configure firewalld:

  • Start and enable firewalld: Ensure that firewalld is running and set to start automatically at system boot. Use the following commands:

    sudo systemctl start firewalld
    sudo systemctl enable firewalld
  • Check the status of firewalld: Verify that firewalld is running using the following command:

    sudo systemctl status firewalld
  • Configure firewalld zones: firewalld uses zones to define different levels of trust for network connections. By default, firewalld provides several predefined zones, such as public, trusted, and block. List the available zones and their settings with the command:

    sudo firewall-cmd --get-zones
  • Assign network interfaces to zones: Assign the desired zone to a network interface using the following command:

    sudo firewall-cmd --zone=zone_name --change-interface=interface_name

    Replace zone_name with the desired zone and interface_name with the network interface name. This ensures that the firewall rules associated with the specified zone are applied to the respective interface.

  • Open ports: Allow incoming network traffic on specific ports using the command:

    sudo firewall-cmd --zone=zone_name --add-port=port_number/protocol --permanent

    Replace zone_name with the desired zone, port_number with the port to open, and protocol with the desired protocol (e.g., tcp, udp). The --permanent flag makes the rule persistent across firewall reloads or system reboots.

  • Reload the firewall configuration: After making changes to the firewall rules, reload the configuration for the changes to take effect:

    sudo firewall-cmd --reload
  • View the firewall configuration: To view the current firewall configuration, including enabled zones, assigned interfaces, and open ports, use the command:

    sudo firewall-cmd --list-all


firewalld is a common firewall technology used in Linux distributions, providing a user-friendly interface for configuring firewall rules, zones, and network interfaces. By understanding the concepts and following the steps outlined in this guide, you will be well-prepared to configure firewalld in your Linux system. Remember to familiarize yourself with the specific commands and configuration settings of firewalld in your distribution.

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