GCIA · Question #73
Which of the following firewalls operates at three layers- Layer3, Layer4, and Layer5?
The correct answer is C. Dynamic packet-filtering firewall. Dynamic packet-filtering firewalls use stateful inspection to track connection context across the Network, Transport, and Session layers, making them operate at Layers 3, 4, and 5.
Question
Which of the following firewalls operates at three layers- Layer3, Layer4, and Layer5?
Options
- ACircuit-level firewall
- BApplication layer firewall
- CDynamic packet-filtering firewall
- DProxy firewall
How the community answered
(37 responses)- A3% (1)
- B11% (4)
- C81% (30)
- D5% (2)
Why each option
Dynamic packet-filtering firewalls use stateful inspection to track connection context across the Network, Transport, and Session layers, making them operate at Layers 3, 4, and 5.
Circuit-level firewalls operate specifically at Layer 5 (Session layer) by validating TCP handshakes, but they do not independently perform filtering at Layers 3 and 4 as a combined function.
Application layer firewalls operate at Layer 7 by inspecting full application protocol payloads such as HTTP or FTP, which is above the Layer 3-5 range in question.
Dynamic packet-filtering (stateful inspection) firewalls maintain a state table of active connections by examining IP addressing at Layer 3, port and protocol data at Layer 4, and session handshake state at Layer 5. This multi-layer awareness allows them to make filtering decisions based on the full context of an ongoing session, not just individual packets in isolation.
Proxy firewalls function at Layer 7 by acting as an intermediary that fully reconstructs application-layer communications, not at Layers 3, 4, and 5.
Concept tested: Stateful inspection firewall OSI layer operation
Source: https://www.nist.gov/publications/guidelines-firewalls-and-firewall-policy
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