Firewall
A firewall is a network security device or software that monitors and controls incoming and outgoing network traffic based on predefined security rules, acting as a barrier between trusted and untrusted networks.
Firewalls are one of the most established and essential components of network security infrastructure. They enforce access control policies by inspecting packets and determining whether to allow or block traffic based on rules defined by administrators. Firewalls can operate at different layers of the network stack, from simple packet filtering at the network layer to deep packet inspection at the application layer.
There are several types of firewalls, including stateless packet filters, stateful inspection firewalls, application-layer gateways (proxy firewalls), and next-generation firewalls (NGFWs). NGFWs combine traditional firewall capabilities with advanced features such as intrusion prevention, SSL/TLS inspection, application awareness, and threat intelligence integration.
Proper firewall configuration is critical to network security. Common misconfigurations include overly permissive rules, failure to restrict outbound traffic, neglecting to update rules when services change, and leaving default policies too open. Organizations should follow the principle of least privilege when crafting firewall rules, regularly audit rulesets, log denied and allowed traffic for analysis, and integrate firewalls into a broader defense-in-depth strategy.