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ISC2 CC A company uses a stateful firewall Practice Question
A company uses a stateful firewall. A user reports that an application requiring multiple dynamic ports is not working. The firewall logs show that packets from the server are being dropped. What is the most likely cause?
⚠ Common exam trap
ISC2 often tests the misconception that a stateful firewall automatically handles all dynamic port protocols, when in fact it requires proper ALG configuration to inspect control channel payloads for port negotiation.
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
✓
The firewall is only allowing packets that match an established session, but the application's control channel is not being tracked correctly.
A stateful firewall tracks sessions by monitoring the control channel. For applications like FTP that use dynamic ports, the firewall must inspect the control channel to dynamically open pinholes for data channels. If the control channel is not tracked correctly, the firewall will not recognize the data channel packets as part of an established session and will drop them, even if the initial control session was allowed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The firewall is only allowing packets that match an established session, but the application's control channel is not being tracked correctly.
Why this is correct
The firewall may not associate the data channel with the control session if it does not inspect the application protocol.
- ✗
The firewall does not have a rule allowing inbound traffic for the application.
Why it's wrong here
If user initiated outbound, stateful firewall should allow return traffic automatically.
- ✗
The firewall is not inspecting application-layer data.
Why it's wrong here
Lack of app-layer inspection can cause issues but stateful firewall may still track by address/port.
- ✗
The firewall's state table is full and cannot track new sessions.
Why it's wrong here
Would affect many sessions, not just this application.
Go deeper
Related to this question
Learn chapter
Access Control Fundamentals
Key term
User
A user is any person, system, or device that interacts with an IT service, resource, or identity system, typically authenticated through credentials and authorized to perform specific actions.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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