Practical Network Scanning

Firewall generations

A firewall is a network security device that monitors and controls all incoming and outgoing network traffic based on a defined and advanced set of security rules. Let's discuss the evolution of firewalls and their capabilities. 

• Packet filtering: First-generation firewalls—these are relatively less expensive with a simple filter function called static packet filtering, also referred to as stateless firewalls. In firewall terminology, stateless refers to rule inspection in both directions in and out; hence, the firewall unit does not maintain any session or connection state.

Basically, packet filtering is performed at Layer 3 (IP) and Layer 4 (Transport) by matching the header fields of the packet against four tuples: ...