linux firewall

Linux Basics: Understanding and Configuring Firewall Rules with iptables, ufw, and firewalld


Firewalls are essential for network security. In a Linux environment, several tools help in setting up and configuring these firewalls. This article will guide you through understanding firewall rules and demonstrate how to manage these rules using iptables, firewalld, and ufw.

What is a Firewall?

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It establishes a barrier between a trusted internal network and untrusted external networks such as the Internet.


Iptables is a user-space utility program that allows a system administrator to configure the IP packet filter rules of the Linux kernel firewall, implemented as different Netfilter modules. The filters are organized in different tables, which contain chains of rules for how to treat network traffic packets.

List all the current rules: iptables -L

Block a specific IP address: iptables -A INPUT -s -j DROP

Allow all traffic on a specific port (e.g., 22 for SSH): iptables -A INPUT -p tcp –dport 22 -j ACCEPT


Firewalld is a front-end controller for iptables used to implement persistent network traffic rules. It’s more user-friendly and suited for beginners or for those who are looking for a more intuitive way to manage firewalls.

Check the status of firewalld: firewall-cmd –state

List all the current rules: firewall-cmd –list-all

Block a specific IP address: firewall-cmd –permanent –add-rich-rule=’rule family=”ipv4″ source address=”″ reject’

Allow all traffic on a specific port (e.g., 22 for SSH): firewall-cmd –permanent –add-port=22/tcp


UFW, or Uncomplicated Firewall, is another front-end controller for iptables, designed to be easy to use while providing the user with powerful options. It’s the default firewall management tool on Ubuntu.

Enable UFW: ufw enable
This will enable the firewall for you on the server. It is critical to note that if you do not whitelist your IP and SSH you will lose access to your server.

Allow traffic on a specific port (e.g., 22 for SSH): ufw allow 22
If you are using a different port than 22 be sure to allow that new port.

Block a specific IP address: ufw deny from

How to Disable UFW: ufw disable
When you disable the firewall please keep in mind that your firewall rules will still be in place. Once you enable it again the firewall rules setup before will be active once again.

How to check the status of UFW: ufw status
As you can see this shows the status of your firewall

How to Reset UFW Firewall Rules

Reset UFW: ufw reset
This command above will reset all of the rules back to default. However, this can block your access again if you do not have SSH ports enabled.

How to Choose a Firewall Tool

Choosing the right tool often depends on your comfort level and the specific needs of your system. Iptables provides comprehensive control but with a complex syntax. On the other hand, ufw and firewalld offer simpler interfaces and are often sufficient for personal use or small scale deployments.

Remember, it’s important to thoroughly test all your rules to ensure that they work as expected and don’t accidentally block important services.

For more helpful guides and information about Linux, please visit our Linux Basics series.



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