A firewall is a network device or software application that usually sits in between the traffic path, inspecting all network traffic. Firewalls are able to block traffic based on certain source/destination IP addresses or port number. Stateful firewalls also keep track of all connections, which allows return traffic to enter the network. Some firewalls also support packet inspection which allows them to look up to the application layer, this allows you to block/permit traffic if it’s from certain websites, block viruses/worms and drop certain payloads. These lessons cover everything that has to do with firewalls.