Firewalls are a tool used to provide critical protection for systems and information. Operating according to a set of configured security rules, firewalls monitor and manage the traffic flowing into and out of your network. It is important to understand the differences between stateful versus stateless firewall technology to ensure that those systems and information is protected.
There are different ways of implementing firewalls. Firewalls can be either network firewalls running on network hardware (a dedicated appliance or integrated into a switch or router); or host-based firewalls that inspect traffic of one or more interfaces of a host computer. When researching firewall types you likely encountered stateful and stateless firewalls. There is also a third firewall type; next-generation firewalls which have become the most common type of commercially available products.
Stateful firewalls are capable of monitoring and detecting states of all traffic on a network to track and defend based on traffic patterns and flows. Stateless firewalls only focus on individual packets, using preset rules to filter traffic.