Top Ten Best Open Source Firewalls in 2021

In this article, we are going to go through some of the best open-source firewalls available in the market. The software includes in the list covers a wide range of security, all the while providing the user comfort and reliability to them. While there is a bridge that you can find between the expensive firewalls and the free-to-use ones. But they share some of the core functions of a firewall. Before we get into the list of best open source firewalls that you should use, keep your network system safe. First, we have to understand what a firewall is? And how is it going to help you keep your computer network safe?


Firewalls have become a common thing to have inside the system either if you are running a single desktop computer as your workstation or ten of them connected to the host server. The firewall works as a layer between all the computers connected to a single router or a LAN port or even to the internet. The best open source firewall makes sure every transaction of data or traffic from the internet goes through the port is well analyzed before going to the destination address. A firewall is a figurative wall that protects the computer from receiving harmful software from getting inside.

With that done, now you are ready to have a list of some of the best open-source firewalls in the market that you can get.

Besides, if you wish to know How to Break a Firewall, and Centos 6 Firewall Functions, as well as the Function of Firewall, here you are.

pfSense – Top 1 Best Open Source Firewall

Best Open Source Firewalls - pfSense

pfSense is one of the popularly used firewall systems by many users. The reason is to provide the user all the functions necessary in the firewall and for being free. The program itself was released back in 2004 and still holds the market to this day. This open-source firewall is easy to use for beginners of networking or professional, experienced workers.

pfSense can be installed on a local machine or on a virtual machine. Users will be in charge of every function in the firewall; pfSense comes with easier to navigate web-based interface. Setting up pfSense is easy and simple, that is one of the reasons why there are so many active users of pf Sense. The devs do really pay attention to the software, as the software receives plenty of new updates to make things run smoother.

Here is the list of functions pfSense is capable of handling.

  • Routing and Firewall
  • VPN from one website to another
  • Blocking of IP address
  • Load Maintenance
  • Proxy Settings
  • OpenVPN

Also, click here to know more about the VMware P2V converter and VMware vSphere Hypervisor.

OPNSense – Top 2 Best Open Source Firewall

Best Open Source Firewalls Opnsense

Here is another addition to the free to use the best open source firewall software. It is one of the beginner-friendly software on the list. The user interface of this software is top-notch, with all the most used settings are on the page, as the user interface looks simple and well categorized. Normally, the developer would fill the entire page with thousands of functions to show up the potential of the software, but that just shows how terrible the design quality is for the software. But here with OPNSense here, you will get a more streamlined user interface. By being beginner-friendly doesn’t make this software application for more advanced professional users.

This software has almost everything that you would expect out of paid software. Some of the function is meant for the beginners, but there are functions that are intended for the professionals. Here are some of the functions you will receive with OPNSense.

  • Setting up the network
  • Monitoring any advancement in the network
  • WAN Load balance
  • VPN Routing
  • Stateful Firewall
  • HTTP load balancer
  • Build-in reporting
  • Up to data Analysis

All of these functions help the user to keep track of every little activity of the network. Which can be very vital for any business. They have a large community with a lot of active members helping out the newcomers.

PS: If you are wondering about the WSUS server and what does a firewall do, or Windows Firewall Allow Ping, just read more here.

UnTangle – Top 3 Best Open Source Firewall

Best Open Source Firewalls - UpTangle

The untangle firewall takes the next step to network security, as they provide a more advanced version. The software can be installed on a server, but the server has to meet the requirement in order to use untangle to its full potential. As I said, the app can be installed on a server, virtual machine, and on the cloud. The software is free to download on your preferable format, iso image, Usb image, or OVA – virtual machine.

Untangle also provides that software in a standalone hardware package. If you don’t want to deal with the initial stage of setting up the firewall, you can just skip all the hassle by picking the hardware version, which comes with the software package pre-installed.

By the way, click here for the comprehensive Proxy vs. Firewall comparison.

ClearOs – Top 4 Best Open Source Firewall

Best Open Source Firewalls - ClearOS

ClearOS is a firewall based on the operation system Linux, that is why this firewall is designed to install only on Linux servers. The firewall carries all the functions that you would expect from a normal firewall.

  • Monitors
  • Control the access to Local services
  • Control the access to applications of the machine

But the clear design of this software is designed to serve only the servers, but clears can also work as network firewalls as well. The user interface looks friendly, as all of the functions in the software are well categorized into tabs. The firewall software is easier to install, and it follows the web-based interface. If you want your firewall to handle more complex rules, there is a custom firewall tool that lets the user add more complex rules such as IPTABLES to the machine. If you think this piece of software is too beginner’s friendly, then there is an advanced version of the firewall out there. Which meant to the server the advanced user of the software. It makes the clearOs the best open source firewall for both beginners and professionals.

IPFire – Top 5 Best Open Source Firewall

Best Open Source Firewalls - IPFire

Here comes another Linux-based firewall that provides security to the networks. It does all the basic functions that you would expect from a normal firewall. It protects the network from the attack from the internet and DoS attacks. The best thing about IPFire is the services you will receive after downloading it. The software is backed by an active community with thousands of members and developers. They always work hard to find a new way to improve the system for better functionality.

IPFire uses an intrusion detection system to evaluate the traffic that the network receives through the internet. If the traffic matches all the things that are expected from an attack, then that particular traffic gets blocked. As you would expect out of the firewall, this one also features a web-based UI for better interaction of the user to the software. If you want to make some rules you are allowed to do it, can make the software work your way, not the other way around.

Here are some of the functions it can perform

  • Web Proxy
  • IDS
  • Proxy and Relay for various protocols
  • Backup server, NFS, Samba, Mail Server
  • VPN termination
  • QoS
  • Wireless Access Point
  • Tor node

When it comes to picking the best open source firewall, you can’t go wrong with IPFire.


IPCop is designed on the Linux based operating system, helps secure the network of the company and home. One of the things that can be a little off-putting about this piece of software is the interface that you have to deal with. In short, there is no interface (GUI); you have to input command lines to make things possible with this software.

While it may require the user to have some coding knowledge to run it on their system, the service this firewall provides is designed for advanced users. The size of the software is just 60 megabytes; if you want to download the software, you can still download it. The software is no longer supported by their developers, but if you want to test it out, you can just visit their website. All these functions make this one of the best open-source firewalls.


Shorewall is another free Linux firewall that comes with a long line of features and functions for the users. This piece of software can only be installed on servers or routers; if you are planning to use your virtual machine or cloud-based service, then you won’t be able to do that. As the firewall service will let the user have an Iptables configuration tool, and the software has enough power to turn the server into a hardware firewall machinery.

Uncomplicated firewall

An uncomplicated firewall is one of the most used firewall software by a lot of users in the world. It is because of the features that it comes with. But the user has to navigate with codes with this software. Which can be a problem for most people.

It depends on the user configuration on how they want their firewall to run in their system. You can manage your Linux Kernel Packet filtering system with this piece of software.


Smoothwall is the best open source firewall that was released all the way back in 2000. This software comes with its very own Linux-based operating system. For display, it has a web-based interface for navigation of various functions. The operating system in this software is tough to withstand any software vulnerabilities on the firewall. It comes with,

  • Lan
  • DMZ
  • Firewalling Internal/ External
  • Web Proxy
  • Records of traffic

The smooth wall community has over 17,000 members on them supporting the software and making it better.

CSF Configserver security

CSF is a stateful firewall, which means it will record everything about the connection for evaluation. Such as the address of the IP, the destination of the address, port number, login detection, and many more to the Linux servers. One of the best things about CSF is the compatibility of the software. It can run on

RHEL/CentOS, Cloud Linux, Fedora, OpenSUSE, Debian, Ubuntu, Slackware, OpenVZ, KVM, VirtualBox, Xen, VMware, Virtuozzo, UML, and many more. With that range of compatibility, you can almost run this firewall on almost anything.


Now you know some of the best open-source firewalls available in the market. Seeing the list will make you wonder why there is so much firewall software in the market because the threat is too high in the climate that we live in today. Each connection carries a lot of valuable information, if not evaluated this information or the connection that carries the information can get attacked. A stronger firewall provides an efficient solution to prevent such things from occurring. That’s why you see so many firewall software in the market with the active community making the software even stronger to prevent more harmful things on the internet. Choose one of the best open-source firewalls that suit you and your system the best.