hardMultiple ChoiceObjective-mapped
CISSP Practice Question: During a security audit, it is discovered that a…
During a security audit, it is discovered that a network firewall is allowing traffic based on source IP address only, without inspecting application-layer data. Which type of firewall is this?
⚠ Common exam trap
Many candidates confuse 'stateful inspection' with 'packet filtering' because both examine IP addresses, but stateful inspection also tracks connection state, whereas the question explicitly states no application-layer inspection and only source IP filtering.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Packet filter
A packet filter firewall operates at Layer 3 (Network) and Layer 4 (Transport) of the OSI model, making decisions solely based on source and destination IP addresses, ports, and protocols. It does not inspect application-layer data (Layer 7), which matches the scenario where traffic is allowed based on source IP address only. This is the simplest and fastest type of firewall, but it lacks the ability to block attacks embedded in application payloads.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Packet filter
Why this is correct
Packet filters operate at the network and transport layers (OSI Layers 3 and 4), making filtering decisions based solely on information contained within the packet header. This includes source and destination IP addresses, port numbers, and protocol types. They are stateless, meaning each packet is evaluated independently without regard for previous packets or the overall connection state, providing a fundamental but limited form of network security.
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Circuit-level gateway
Why it's wrong here
Circuit-level gateways function at the session layer (OSI Layer 5), establishing a virtual circuit between the internal and external hosts. Their primary role is to validate the TCP three-way handshake to ensure the legitimacy of session establishment. While they act as a proxy, they do not perform deep inspection of the packet payload or extensive analysis of individual packet headers beyond the initial connection parameters, focusing instead on session integrity.
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Application gateway
Why it's wrong here
Application gateways, also known as proxy firewalls, operate at the application layer (OSI Layer 7) and act as an intermediary for specific application protocols. They terminate the client's connection, inspect the application-layer data for malicious content or policy violations, and then establish a separate connection to the destination server. This deep content inspection provides the highest level of security but can introduce latency and requires protocol-specific proxies.
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Stateful inspection
Why it's wrong here
Stateful inspection firewalls maintain a state table that tracks the context of active network connections, operating primarily at the network and transport layers. Unlike stateless packet filters, they can differentiate between legitimate incoming traffic that is part of an established session and new, unsolicited connection attempts. This allows them to make more intelligent and dynamic filtering decisions based on the connection's history and state, significantly enhancing security over basic packet filtering.
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Learn chapter
Security Governance and Principles
Key term
Firewall
A firewall is a network security system that monitors and controls incoming and outgoing traffic based on predetermined security rules to protect trusted internal networks from untrusted external networks.
Key term
Audit
An audit is a systematic, independent review of IT systems, processes, and controls to verify compliance with policies, standards, and regulations.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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