CompTIA Security+ All-in-One Exam Guide (Exam SY0-301), 3rd Edition, 3rd Edition

Firewalls

Arguably one of the first and most important network security tools is the firewall. A firewall is a device that is configured to permit or deny network traffic based on an established policy or rule set. In their simplest form, firewalls are like network traffic cops; they determine which packets are allowed to pass into or out of the network perimeter. The term firewall was borrowed from the construction field, in which a fire wall is literally a wall meant to confine a fire or prevent a fire’s spread within or between buildings. In the network security world, a firewall stops the malicious and untrusted traffic (the fire) of the Internet from spreading into your network. Firewalls control traffic flow between zones of network traffic; ...