Which is a primary function of a firewall on an enterprise network?

A firewall's primary function is to enforce security policies by controlling network traffic. It examines incoming (ingress) and outgoing (egress) traffic against a predefined set of rules to determine whether to allow or deny its passage. This protection extends to both internal network segments and external connections. While firewalls can be part of a default gateway setup, their core role isn't solely to be the gateway itself. Modern firewalls often use stateful inspection, not just stateless, to track connections and make more intelligent decisions. While a firewall is often placed at the network edge, acting as an intermediary between the enterprise and the ISP is a broader function of a router or gateway, with the firewall providing the security layer.