IPFire is one of Linux Distro that specialized to be a router/firewall.
Installing IPFire is very easy, just follow the instruction at wiki.ipfire.org/en/installation/start.
The very simple type of installation is Green - Red type. Green means your internal network and Red means your external network. You have to use private IP for Green, such as 192.168.0.x and you can assign the Green network Card as 192.168.0.1 and use DHCP server enable for Green network.
For the IP Address of Red Network Card, you have to ask your Internet Service Provider. And the informations you must know are Default Gateway, DNS server if your internet connection use static IP Address.
After successful installation, you can connect to IPFire router machine through other computer that connected to Green network card. Then launch internet browser and go to https://192.168.0.1:444/cgi-bin/proxy.cgi.
After successful login to web-based administration panel of your IPFire router, you will see many feature that you can apply for your new router/firewall.
For example, I figure out some features that applied in my IPFire router/firewall.
To boost internet connection, I enable Web Proxy, with transparent on Green. Go to Network menu then choose webproxy. So many options you can enable here. I enable URL Filter to block porn sites and facebook during office hours. To see the complete list of site categories for URL Filter go to Network >> Content Filter. I also enable download throttling to limit download speed for each computer on Green Network.