The answer is that the FTP application requires additional configuration for passive mode, which is why the traffic remains blocked despite an allow rule. FTP uses two separate channels: a control channel on TCP 21 and a data channel on a dynamically negotiated high port. In passive mode, the client initiates the data connection, but the firewall must inspect the control channel’s application-level negotiation to dynamically open a temporary pinhole for that random data port; without this deep packet inspection, the data channel is dropped even when the control channel is allowed. On the PCNSA exam, this tests your understanding of how Palo Alto Networks’ App-ID decoders handle multi-channel protocols like FTP—a common trap is assuming a simple allow rule for the application covers all traffic, when in fact the firewall must see the control channel’s PASV command to permit the data flow. Memory tip: think “PASV opens the pinhole”—if the firewall can’t inspect the PASV command, the data channel gets blocked.
PCNSA Device Management and Services Practice Question
This PCNSA practice question tests your understanding of device management and services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
A network administrator wants to allow FTP traffic from the internal network to a specific external server. The administrator creates a security policy rule with source zone 'internal', destination zone 'external', destination IP of the server, and application 'ftp'. However, the traffic is still blocked. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The FTP application requires additional configuration for passive mode
FTP uses two separate channels: a control channel (TCP 21) and a data channel. In passive mode, the client initiates both connections, but the data channel uses a random high port negotiated via the control channel. The Palo Alto Networks firewall's application decoder for FTP must inspect the control channel to dynamically open pinholes for the data channel; without this, the data connection is blocked even if the control channel is allowed. Option D is correct because the administrator likely created a rule for application 'ftp' but did not ensure that the FTP application's passive mode data connections are properly handled, which requires the firewall to perform application-level inspection and create temporary security policy openings for the negotiated data ports.
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.
Logging does not affect whether traffic is allowed.
✗
The rule is set to deny instead of allow
Why it's wrong here
The administrator created the rule to allow.
✓
The FTP application requires additional configuration for passive mode
Why this is correct
FTP uses dynamic ports; the firewall needs to inspect control channel to allow data channel.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a simple 'allow' rule for the application 'ftp' is sufficient, overlooking that FTP's dual-channel nature requires the firewall to perform deep packet inspection to dynamically permit the data channel ports negotiated in passive mode.
Detailed technical explanation
How to think about this question
FTP passive mode (PASV) is defined in RFC 959 and requires the server to listen on a random port (typically above 1023) for data connections, which the client connects to after receiving the port number in the control channel. Palo Alto Networks firewalls use Application Override or Application-ID to decode FTP control traffic and dynamically create temporary security policy entries (pinholes) for the negotiated data ports; if the application decoder is not properly enabled or the rule does not match the application correctly, the data channel traffic is dropped. In real-world scenarios, this often manifests as successful login but failure to list directories or transfer files, leading administrators to mistakenly think the rule is insufficient.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
Device Management and Services — This question tests Device Management and Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The FTP application requires additional configuration for passive mode — FTP uses two separate channels: a control channel (TCP 21) and a data channel. In passive mode, the client initiates both connections, but the data channel uses a random high port negotiated via the control channel. The Palo Alto Networks firewall's application decoder for FTP must inspect the control channel to dynamically open pinholes for the data channel; without this, the data connection is blocked even if the control channel is allowed. Option D is correct because the administrator likely created a rule for application 'ftp' but did not ensure that the FTP application's passive mode data connections are properly handled, which requires the firewall to perform application-level inspection and create temporary security policy openings for the negotiated data ports.
What should I do if I get this PCNSA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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