A firewall is a computer tool (hardware and/or software) designed to protect the data on a network. It will monitor and filter incoming and outgoing network traffic based on security policies previously established by the company.

A firewall represents the barrier between a private internal network and the public Internet. Its purpose is to filter dangerous traffic.

Firewall - copyright @ wikipedia

General operation

The firewall is until the last few years considered as one of the cornerstones of the security of a computer network. It allows to apply an access policy to network resources. Generally, the trusted areas include the Internet and at least one internal network.

The filtering is done according to various criteria. The most common ones are :

A firewall often acts as a router and thus makes it possible to isolate the network into several security zones called demilitarized zones or DMZs.

Router firewall, with a DMZ
Router firewall, with a DMZ - copyright @ wikipedia

The different types of firewall

New features

Recent firewalls include more and more features:

The limits of the firewall

Firewalls are not an absolute protection against cyber attacks. In fact, their effectiveness only comes from their configuration and their role as an intermediary between communications.