How does a firewall filter traffic?

How many types can a firewall be? Firewalls can be classified as software or hardware firewalls. The software firewall is a program installed on a PC that analyzes traffic through port numbers or applications, while the physical firewall is a professional device that connects the gatway and the network, being integrated into broadband routers. Software firewalls are often implemented by default on operating systems, a good example being Windows Firewall. How does a firewall filter traffic? Method 1. Packet filtering One of the best known methods is packet filtering, called stateless firewall. This filter checks the Transport Control Protocol (TPS) traffic. Metoda 2. Proxy Server A proxy server intercepts and modifies incoming and outgoing data so that it does not display the actual network address. Proxy servers act as an intermediary between the two ends of a client / server network connection. They interact with network applications, most commonly with web browsers and servers. Proxy servers work at the application level (layer 7) of the OSI model and are also more difficult to install. Method 3. Gateway application A proxy gateway is a module that receives requests for web services and forwards them to an endpoint, defined in a proxy group. Gateway is an automatic filtering technique that analyzes transmitted data. The main disadvantage of the gateway is that it can adversely affect the performance of the system. In conclusion, before using a firewall you need to follow a few simple steps: to choose the services that must be offered by the firewall; to desegregate the groups of users that will be protected; to define the degree of protection that each group of users needs and how the necessary protections will be implemented