OSI-licensed open source
Open-source firewalls give small businesses, homelabs and IT teams a network gatekeeper without per-seat licensing. This page covers full firewall and router distributions (OPNsense, pfSense, VyOS, OpenWrt), host firewall management (firewalld), and the intrusion detection and prevention engines that turn a firewall into a next-generation or UTM-style setup (Suricata, Snort 3, CrowdSec).
We only list projects with OSI-approved licences confirmed on their repositories. Note that a true UTM appliance is usually a firewall distribution combined with an IDS/IPS and add-on packages, so we explain where each tool fits.
Tools, licences and pricing checked against vendor and repository pages on November 7, 2026.
| Tool | Best for | Pricing | Licence |
|---|---|---|---|
| OPNsense | Full firewall and router with a modern GUI | Free, open source | BSD-2-Clause |
| pfSense CE | Established firewall appliance deployments | Free, open source (Community Edition); commercial Plus and hardware, See vendor pricing | Apache-2.0 |
| VyOS | Scriptable routing and firewall configuration | Free, open source rolling release; subscription builds, See vendor pricing | LGPL-2.1 |
| OpenWrt | Router and edge firewall on embedded hardware | Free, open source | GPL-2.0-only |
| firewalld | Host-based firewalling on Linux servers | Free, open source | GPL-2.0-only |
| Suricata | IDS/IPS and network monitoring alongside a firewall | Free, open source | GPL-2.0-only |
| Snort 3 | Rule-based intrusion prevention | Free, open source | GPL-2.0-only |
| CrowdSec | Collaborative IP reputation and automated blocking | Free, open source; paid plans, See vendor pricing | MIT |
Best for: Full firewall and router with a modern GUI · Free, open source
OPNsense is an open-source firewall project whose core repository holds the GUI, API and systems backend. It is built around a web interface and package-based extensions.
Best for: Established firewall appliance deployments · Free, open source (Community Edition); commercial Plus and hardware, See vendor pricing
pfSense is a firewall operating system built on FreeBSD with a custom kernel and a web interface. It began in 2004 as a fork of m0n0wall.
Best for: Scriptable routing and firewall configuration · Free, open source rolling release; subscription builds, See vendor pricing
VyOS is an open-source network operating system providing routing and firewalling. The vyos-1x repository holds its command definitions, configuration scripts and a Python library.
Best for: Router and edge firewall on embedded hardware · Free, open source
OpenWrt is a Linux operating system for embedded devices with a writable filesystem and package management. It is widely used to turn routers into configurable firewalls.
Best for: Host-based firewalling on Linux servers · Free, open source
firewalld is a firewall manager for Linux hosts that assigns connections and interfaces to zones with trust levels and changes rules at runtime. It supports IPv4, IPv6 and ethernet bridges.
Best for: IDS/IPS and network monitoring alongside a firewall · Free, open source
Suricata is a network security engine that detects and can block intrusions and supports network security monitoring. It is developed by the OISF and the community.
Best for: Rule-based intrusion prevention · Free, open source
Snort++ is a next-generation intrusion prevention system supporting multiple packet processing threads and pluggable components. Its repository states it is governed exclusively by GPL v2.
Best for: Collaborative IP reputation and automated blocking · Free, open source; paid plans, See vendor pricing
CrowdSec is an open-source, community-driven security project. Its Security Engine acts as an IDS/IPS and WAF that detects bad behaviour from logs and HTTP requests, with bouncers and a community blocklist for remediation.
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| If you need… | Start with |
|---|---|
| Full firewall appliance with a polished web GUI | OPNsense, pfSense CE |
| Scriptable routing and firewall as code | VyOS |
| Turn a consumer router into a firewall | OpenWrt |
| Firewall rules on Linux servers | firewalld |
| Intrusion detection or prevention | Suricata, Snort 3 |
| Automated blocking from log behaviour | CrowdSec |
Quick answers to common questions
OPNsense and pfSense CE are the common full-appliance choices; VyOS and OpenWrt suit routing-focused or embedded setups.
Often yes: pair a firewall distribution with an IDS/IPS such as Suricata and add VPN and filtering packages, though you assemble and maintain the stack yourself.
Both are FreeBSD-based with web GUIs. OPNsense is BSD-2-Clause licensed; pfSense CE is Apache-2.0 and has a separate commercial Plus edition. Test both on your hardware.
Only projects with an OSI-approved licence confirmed on their repository are listed. Products with proprietary or source-available components are left out.
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