What is the primary role of a firewall in an enterprise network?

A firewall's primary role is to act as a security barrier, controlling traffic flow between different network segments, typically between a less trusted external network (like the internet) and a more trusted internal network. It uses a set of predefined rules to inspect incoming and outgoing packets and decides whether to permit or deny them based on criteria like source/destination IP addresses, ports, and protocols. "Process unauthorized packets and forward them to less secure segments" is incorrect because unauthorized packets are typically dropped, not forwarded. "Forward packets using stateless packet inspection" is too narrow; modern firewalls often use stateful inspection, which is more robust. "Deny all packets from entering the administrative domain" is incorrect as it would prevent legitimate traffic, making the network unusable.