How to Set Up and Manage Firewalls on Linux Systems

• A firewall in Linux is a security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

• Linux uses several tools for firewall management, with iptables and firewalld being two of the most common.

• It can be used to block access to different IP addresses, Specific subnets, ports (virtual points where network connections begin and end), and services.

Types of Linux Firewalls :

1. iptables

• Description: iptables is the most traditional and widely-used Linux firewall tool. It interacts directly with the Linux kernel's netfilter subsystem to manage incoming and outgoing traffic using rules.

• Features:

  • Works by organizing rules into tables (filter, nat, mangle, etc.) and chains (INPUT, OUTPUT, FORWARD).

  • Can filter traffic by IP, port, protocol, and other parameters.

  • Supports NAT (Network Address Translation) for modifying packet addresses.

• Use Case: Ideal for complex firewall configurations requiring manual rule definitions.

2. firewalld

• Description: firewalld is a dynamic firewall manager that offers an abstraction layer over iptables. It uses predefined zones (such as public, private, work) to assign different levels of trust to network connections.

• Features:

  • Offers easy and dynamic configuration of firewall rules.

  • Supports IPv4, IPv6, Ethernet bridges, and ipsets.

  • Zones simplify applying rules to different network environments.

  • Has a GUI interface for managing firewall rules.

• Use Case: Best for users who want an easier, more flexible tool for managing firewall rules.

3. nftables

• Description: nftables is the modern replacement for iptables. It improves performance and usability by providing a simpler, unified syntax for packet filtering and classification. It also uses the netfilter framework.

• Features:

  • Unified handling of IPv4, IPv6, and Layer 2 traffic (such as Ethernet).

  • Simpler rule sets compared to iptables.

  • Better performance with reduced system overhead.

  • Uses rulesets to define filtering actions, replacing iptables chains and tables.

• Use Case: Ideal for new deployments or upgrades from iptables that need better performance and easier syntax.

4. Uncomplicated Firewall (UFW)

• Description: UFW is a simple and user-friendly firewall interface built on top of iptables. It is used mainly in Ubuntu-based distributions to simplify the creation of firewall rules.

• Features:

  • Simplifies basic firewall management, making it more accessible to non-expert users.

  • Designed to manage typical use cases like allowing or denying services by port or protocol.

  • Offers logging of dropped packets and other events.

• Use Case: Best for users who want simple command-line control over their firewall without needing to write extensive rules.

Commands Firewalld:

• • To check status:

        sudo firewall-cmd --state
    

    • To list all rules:

        sudo firewall-cmd --list-all
      

    • To allow a service/port:

        udo firewall-cmd --add-service=http --permanent
        sudo firewall-cmd --reload
      

Configuring firewalld :

firewalld provides a more dynamic and easier way to manage firewall rules through zones.

Step 1 : Check Current firewalld Status

sudo firewall-cmd --state

Step 2: Check Active Zones

sudo firewall-cmd --get-active-zones

Step 3: Set Default Zone

The default zone is applied to all network interfaces unless specified otherwise.

sudo firewall-cmd --set-default-zone=public

Step 4: Allow Services in a Zone

You can open ports or allow services like HTTP, HTTPS, and SSH in a specific zone (e.g., public):

sudo firewall-cmd --zone=public --add-service=http --permanent
sudo firewall-cmd --zone=public --add-service=https --permanent
sudo firewall-cmd --zone=public --add-service=ssh --permanent

Step 5: Allow Specific Ports

You can open specific ports (e.g., for a custom application):

sudo firewall-cmd --zone=public --add-port=8080/tcp --permanent

Step 6: Reload firewalld

After making changes, reload the firewall to apply them:

sudo firewall-cmd --reload

Step 7: Check Active Rules

To view your current rules:

sudo firewall-cmd --list-all

Advantages And Disadvantages Of Firewall

Conclusion

In this article, we have discussed Linux Firewall, and how to configure Linux firewall. Linux is based on Unix-like which has a modular design. To protect our system, we have a Linux firewall and firewalld. We will discuss the different types of Linux firewall and their rules. In the end, we learned about how to configure a firewalld. By understanding this article one can secure their Linux system with the required firewall configuration.