What is a Firewall in Today's World?
The firewall, which we can also define as a digital firewall; is a network security system that controls incoming and outgoing data packets to and from the network, based on software and hardware, within the framework of certain rules. Depending on the filter it uses while controlling the network, it always passes the internet traffic through controls such as IP filtering, port filtering, web filtering, content filtering.
Most operating systems today use their own software-based firewall system. At the same time, routers that transfer data between networks also have their own firewall systems. Although the widespread use of the Internet and computers is a fairly new situation, firewall security systems are a technology that emerged in the 1980s.
What Does Firewall Do?
Firewall network security systems, which work as hardware or software bases, examine incoming and outgoing data packets to the network with a predetermined filter. The main purpose is to prevent possible attacks by passing data packets from unsafe sources through this filter.
Firewall network security systems are located on ports where data is shared over the network with external devices. "Source address 172.18.1.1 is allowed to reach destination 172.18.2.1 over port 22." The definition most accurately describes the work these digital firewalls do.
How Firewall Works
Let's go through an example to understand how firewall network security systems work; Let's think of IP addresses as houses and port numbers as rooms. Only secure people, that is, secure source addresses can enter the house. People entering the house can only reach certain rooms, namely connection points, bypassing through another filter. In other words, the firewall filter provides control and supervision at multiple points.
The old-style packet filtering firewall security network systems were a bit weak in this regard. They checked the data packets through a basic filter and sometimes accepted the request directly from the trusted source. As it became clear over time that not every request from a reliable source was in good faith, firewall network security systems were developed and different types emerged. Finally, I recommend following this resource for firewall projects.