pfSense 2.5.1 was released in early 2021. While it was a stable release that brought significant updates (such as full support for WireGuard and PHP 7.x), it has since been superseded by the 2.6.x branch and, more recently, the major 23.x/24.x "Plus" releases.
However, Netgate has removed older CE versions from the main landing page to push users toward pfSense Plus or the latest CE. Fortunately, the files remain accessible via direct URL if you know the naming convention. pfsense 251 download iso link
Access the web GUI by connecting a computer to the LAN port and navigating to https://192.168.1.1 (default credentials: admin / pfsense ). How To Install pfSense + Beginners Configuration Guide pfSense 2
You are likely here for the "pfsense 251 download iso link" because you need a specific driver or plugin. However, you must understand the risk: Fortunately, the files remain accessible via direct URL