"Building your own firewall is a great achievement when you're ready to leave consumer units or ISP-provided hardware. There are a few software options available, but we recommend giving OPNsense a go. Just about anything with a compatible processor can run OPNsense, everything from used enterprise servers to a single-board computer (SBC). So long as you can have two Network Interface Cards (NICs) for WAN and LAN gateways, you're good to go.
I picked up an affordable $150 fanless mini PC with an Intel N3700 processor and four 2.5Gb Ethernet ports. After adding a small boot SSD and 16 GB of RAM, the firewall was ready for OPNsense to be installed. The entire process took less than 10 minutes from start to finish, and I had a new network up and running within half an hour. Though not perfect (I would like to move to a new system with 10Gb SFP links), it's proven to be reliable enough for keeping the LAN alive for almost a year.
This is something that isn't often associated with networking, but creating something from scratch can be incredibly rewarding. It's why the home lab has become such a popular hobby and why more people are looking to self-host as much as possible. It's a great way to learn something new, develop new skills, and be rewarded with a notably more capable LAN that's not only more secure, but can be configured in such a way as not possible with standard routers."
Source: XDA
