Which network appliance inspects packet state to determine whether a packet is allowed?

A firewall inspects packet state, such as source/destination IP addresses, port numbers, and protocol types, to determine if a packet is part of an established, allowed connection or if it should be blocked based on predefined security rules. This stateful inspection is a core function of modern firewalls. A Layer 2 switch operates at the data link layer and forwards frames based on MAC addresses, without inspecting packet state. A LAN controller manages wireless access points and client connections but doesn't perform stateful packet inspection for security. A load balancer distributes network traffic across multiple servers to optimize resource utilization and maximize throughput, not primarily for security inspection.