A firewall is a network security system that monitors the inbound and outbound network traffic of a system and filters it according to some predetermined rules. It can be implemented as hardware or as software. If configured properly, a firewall can prevent network intrusions up to a great extent.

What are the First Generation of Firewalls or The Packet Filters?

This type of firewall was first developed in the 1980s. They mainly monitor network addresses and ports of inbound and outbound network traffic and filter them as per some predetermined rules.

They store no information on the connection state. Instead, they inspect source IP addresses, destination IP addresses, source and destination ports, and protocols like TCP, UDP, etc, to filter the traffic.

This type of firewall mainly works in the first three layers of the OSI model—the physical layer, the network layer, and the transport layer—and can monitor the source and destination ports. As Packet Filters do not store any information on the connection state, they cannot filter traffic depending on whether a particular network packet is part of an existing stream of traffic.

What are the Second Generation of Firewalls or The Stateful Filters?

This type of firewall was first developed in the early 1990s. It retains network packets until it gets enough information on the connection state of the packet. Then, it determines whether a packet is part of an existing connection and filters the traffic accordingly.

Second-generation firewalls can operate up to layer 4 of the OSI model, enabling stateful packet inspection.

What are the Third Generation of Firewalls or The Application Layer Firewalls?

This type of firewall was first developed in the mid-1990s. Till now, firewalls were able to filter traffic based on IP addresses, ports, or connection states, but they were unable to understand application layer protocols like HTTP, FTP, and DNS. As a result, they could not detect whether an unwanted protocol is trying to bypass the firewall on an allowed port or whether any protocol is getting abused. The Application Layer Firewalls can monitor and understand certain application layer protocols and filter traffic as per that.

Interested readers will get more information on this in What is Web Application Firewall?

What are Next Generation Firewalls and Deep Packet Inspection?

The Next Generation Firewall or NGFW is a recently developed integrated network platform that combines a traditional firewall with other security system functionalities like an application …