A Step-By-Step Guide on How to Configure a Firewall in Linux
Understanding what a firewall is and how it works:
A firewall is a program that surrounds the interface between a private network and the rest of the big and (usually) bad internet. You can think of the firewall as a gateway. It follows pre-configured rules that allow certain traffic to pass through from the internet to the private network and blocks those that are unwanted and potentially harmful.