This is one of the 52 terms in The Language of Cybersecurity published by XML Press in 2018 and the contributor for this term is Sarah Granger.

What is it?

A network security system built into hardware or software that monitors network traffic and controls incoming and outgoing traffic based on a set of rules.

Why is it important?

Firewalls enable system administrators to monitor and control network traffic coming into and out of their systems. Firewalls provide a first line of defense against network-based cybersecurity attacks. They are also used to censor information by blocking traffic to and from certain sites.

Why does a business professional need to know this?

Firewalls first came into use as packet filters that analyzed data in packets and identified which data was safe to continue moving forward and which data needed to be removed or stopped. Up to that point, network administrators had to choose between keeping networks connected to the internet, allowing most data to come and go, or disconnecting networks completely, leaving them physically isolated.

Modern firewalls work in hardware and software through an established set of rules to determine what comes in and what goes out. Firewalls are considered a first line of defense against unwanted intruders, information, or code. They can be used to keep out hackers or merely to cut down on spam.

Two common types of firewalls are network firewalls, which monitor and filter communications between networks (e.g., between an internal corporate network and the external internet), and host-based firewalls, which monitor and filter communications coming in and out of an individual computer. A firewall can block a communication packet based on the port it attempts to pass through or the type of content it contains.

The most famous firewall is the Great Firewall of China, which the Chinese government uses to block people inside China from accessing sites and services containing information prohibited by the government. Google, for example, is blocked in China, so Chinese internet users generally must use the Chinese internet search engine Baidu, which operates through censorship filters. The Chinese firewall has been surprisingly successful at blocking vast amounts of information.