Firewall

A security device or software that monitors network traffic and allows or blocks it according to rules, acting as a barrier between trusted and untrusted networks.

A firewall sits between your internal network and the internet, deciding which connections are allowed. Business-grade firewalls often include extra features such as intrusion prevention, web filtering, VPN access and the ability to inspect traffic for threats. Computers also have built-in software firewalls, such as Windows Defender Firewall, that protect each device individually.

A firewall is only as good as its configuration and maintenance. Rules added for a temporary project and never removed, open remote access ports, default administrator passwords and outdated firmware are common problems. Firewalls and VPN appliances themselves are frequent targets for attackers, so an unpatched firewall can become an entry point rather than a barrier.

Practical tip: have your firewall rules reviewed at least once a year and remove anything that is no longer needed. Keep the firmware updated, protect the management interface with multi-factor authentication, and make sure the device is still supported by its manufacturer. A consumer router is rarely an adequate firewall for a business.