What is a firewall?

A firewall is fundamentally a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Its primary function is to establish a barrier between a trusted internal network and untrusted external networks, such as the internet. By doing this, firewalls help protect networks from unauthorized access, cyberattacks, and various threats, ensuring that only legitimate traffic is allowed through.

Firewalls can be either hardware-based, in the form of dedicated devices that filter data at the network level, or software-based, which typically run on individual computers and protect against threats at the operating system level. They can be configured to block or allow traffic based on specific criteria, such as IP addresses, domain names, protocols, and ports.

In contrast, other choices like web application creation, malware, and network performance assessment do not align with the primary purpose of a firewall. They focus on different aspects of technology and security that are not directly related to the monitoring and control of network traffic, which is the core function of a firewall.