The term ‘open source firewall’ is actually two different terms mashed together. A firewall is a software barrier to the outside world; it blocks information that may be harmful to the computer system. Open source is both a type of software and a software movement that allows free access to software and the code in which it is written. In general, an open source firewall is easier to find for a Linux® system, or a similar open source operating system, than a commercial system such as Windows® or MacOS®.
Firewalls protect computer systems from harmful information. A firewall may be a piece of hardware or software, but ‘open source firewall’ implies that it is software. A software firewall is an installed program on a computer, unlike a hardware firewall that typically exists separate from the computer. Firewalls sit between the local network and the outside network. If the local network has multiple machines, only ones that talk directly to the outside need firewall software.
Open source both describes the software’s origin and the mentality behind it. In all open source software, the code and usage licenses are available to the public. This allows other programmers to see exactly how a piece of software functions, or even borrow code for use in their own projects. While the availability of the source code seems like it would make an open source firewall more vulnerable, this generally isn’t the case. The community constantly finds vulnerabilities and patches for them, often faster than commercial software companies.
With standard software, the end goal is to make money—other goals often take a second position to that one. The end goal for open source developers isn’t always as clear. Sometimes it is used as self-promotion, such as an open source product that works well with one of the company’s commercial products. Other times, it is a small group that comes up with a product either for the recognition or to fill a void they see in the software community.
With all that in mind, an open source firewall is protective software built with the community in mind. As with most open source software, it is most common on an open source operating system such as Linux®. Firewalls such as Endian Firewall® or SmoothWall Express® are free, open source and generally easy to use. While commercial operating systems, like Windows® or MacOS®, have free firewalls, they often aren’t open source. These freeware firewalls are common on commercial systems, but do not have source code available to their users.