Firewall theory Introduction Firewalls Protocols Paket structure Request and Response Filtering by address ICMP TCP and UDP Filtering by port Network interfaces Bad packets Conclusion Introduction Gone are the days when we could live our lives without the Internet. It became our “go to” place when looking for fun, information or business. But there are also nefarious actors on this largest computer network. Their goal is often gaining access to information, damaging systems and (most importantly) penetrating into systems with the intention to gain control and use them as a launching pad for further activities. There are no commands int