Which of the following types of firewall ensures that the packets are part of the established session?

Switch-level firewall is not a recognized standard firewall classification and does not describe a type that performs session state tracking.

An application-level firewall (proxy firewall) inspects packet payload content at Layer 7 but is not primarily defined by tracking session state across individual packets.

A stateful inspection firewall maintains a state table recording source and destination IP addresses, ports, TCP sequence numbers, and connection states for every active session. Each packet is checked against this table, and packets that do not correspond to a known, established connection are dropped, preventing spoofed or out-of-state traffic from entering the network.

A circuit-level firewall validates the TCP three-way handshake at the session layer but does not continue inspecting subsequent packets to confirm they remain part of the established session.