Which of the following types of firewall functions at the Session layer of OSI model?

Question

Options

• ACircuit-level firewall
• BApplication-level firewall
• CPacket filtering firewall
• DSwitch-level firewall

• A
  87% (34)
• B
  3% (1)
• C
  3% (1)
• D
  8% (3)

Explanation

Circuit-level firewalls operate at Layer 5 (Session layer) of the OSI model by monitoring TCP handshakes and session establishment to determine whether a connection is legitimate - without inspecting the actual packet contents.

Why the distractors are wrong:

• B (Application-level/proxy firewall) operates at Layer 7 (Application layer), inspecting full application data like HTTP or FTP traffic.
• C (Packet filtering firewall) operates at Layer 3–4 (Network/Transport layers), examining IP addresses and port numbers only.
• D (Switch-level firewall) is a fabricated term - switches operate at Layer 2 (Data Link), and this is not a recognized firewall category.

Memory tip: Think "Circuit = Connection = Session" - circuit-level firewalls care about whether a session/connection is valid, which maps directly to the Session layer. The word "circuit" itself implies an established communication path, the core concept of Layer 5.

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