Firewalls act as barriers that inspect network traffic and decide what to allow or block according to predefined rules. The article explains how the concept evolved from fire-resistant building barriers into a core computing security measure, and why different firewall designs suit different protection needs.

– Packet-filtering firewalls assess packets using details such as IP addresses, ports and protocols, but do not recognise whether packets belong to legitimate connections.
– Stateful inspection firewalls track active connections, allowing packets associated with trusted sessions and improving security.
– Proxy and application-level firewalls act as intermediaries and inspect traffic contents in greater detail, though they require more processing.
– Next-generation firewalls combine traditional filtering with features including intrusion prevention and deep packet inspection.