- A
Packet filter firewall
Why wrong: Packet filters operate at L3/L4 and do not inspect application data.
- B
Circuit-level gateway
Why wrong: Circuit-level gateways operate at Layer 5 (session) and do not inspect application data.
- C
Application proxy firewall
Application proxies terminate and re-establish connections, allowing full inspection.
- D
Stateful inspection firewall
Why wrong: Stateful firewalls track connection state but do not inspect application content.
Question 744 of 1,000
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which type of firewall can inspect the contents of application-layer traffic, such as HTTP requests, and block malicious payloads?
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
✓
Application proxy firewall
An application proxy firewall (also known as an application-level gateway) operates at Layer 7 of the OSI model and can fully inspect the content of application-layer protocols such as HTTP, FTP, and SMTP. By terminating the client connection and establishing a separate connection to the server, it can parse and validate the payload—for example, examining HTTP request bodies for SQL injection strings or malicious scripts—and block them before they reach the internal server. This deep inspection capability distinguishes it from lower-layer firewalls that only examine headers or connection states.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 firewall
Why it's wrong here
Packet filters operate at L3/L4 and do not inspect application data.
- ✗
Circuit-level gateway
Why it's wrong here
Circuit-level gateways operate at Layer 5 (session) and do not inspect application data.
- ✓
Application proxy firewall
Why this is correct
Application proxies terminate and re-establish connections, allowing full inspection.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Stateful inspection firewall
Why it's wrong here
Stateful firewalls track connection state but do not inspect application content.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a stateful inspection firewall (which tracks connection state) with an application proxy firewall, mistakenly believing that stateful inspection includes deep payload analysis, when in fact stateful inspection only monitors packet headers and connection state at Layers 3 and 4.
Detailed technical explanation
How to think about this question
Under the hood, an application proxy firewall acts as a full proxy: it receives the client's HTTP request, terminates the TCP connection, then reconstructs the entire application-layer message (including headers and body) before forwarding it. This allows it to enforce granular rules, such as blocking HTTP methods like PUT or DELETE, or filtering based on MIME types or specific patterns in the payload (e.g., regex for <script> tags). In real-world scenarios, this is critical for protecting web servers from attacks like cross-site scripting (XSS) or command injection, which packet filters and stateful firewalls cannot detect.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this CISSP question test?
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Application proxy firewall — An application proxy firewall (also known as an application-level gateway) operates at Layer 7 of the OSI model and can fully inspect the content of application-layer protocols such as HTTP, FTP, and SMTP. By terminating the client connection and establishing a separate connection to the server, it can parse and validate the payload—for example, examining HTTP request bodies for SQL injection strings or malicious scripts—and block them before they reach the internal server. This deep inspection capability distinguishes it from lower-layer firewalls that only examine headers or connection states.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jul 4, 2026
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.
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