The answer is that the traffic is not matching the expected application 'web-browsing'. This occurs because the Palo Alto Networks firewall uses application identification (App-ID) to classify traffic based on packet signatures, and when the initial packets do not match the signature for the application defined in the security rule—such as 'web-browsing'—the session state remains 'incomplete' until enough data is inspected or the traffic is dropped. On the PCNSA exam, this scenario tests your understanding of how App-ID processes the first few packets and why an application incomplete state reason often points to a mismatch between the actual traffic and the rule’s application object, especially with non-standard HTTP headers or encrypted payloads. A common trap is assuming the firewall will allow any HTTP traffic on port 80, but the rule specifically requires the application to be identified as 'web-browsing'. Memory tip: think of App-ID as a bouncer checking IDs—if your traffic doesn’t show the right badge, it stays in the "incomplete" waiting room.
PCNSA Palo Alto Networks Platforms and Architecture Practice Question
This PCNSA practice question tests your understanding of palo alto networks platforms and architecture. 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.
Exhibit
Refer to the exhibit.
show system info | match model
vm-series
show running security-policy
set rulebase security rules "Allow-Web" from [ trust ] to [ untrust ] source [ 10.0.0.0/24 ] destination [ any ] application [ web-browsing ] service [ application-default ] action allow
set rulebase security rules "Block-All" from [ any ] to [ any ] source [ any ] destination [ any ] application [ any ] service [ any ] action deny
show running nat-policy
set rulebase nat rules "NAT-Internet" from [ trust ] to [ untrust ] source [ 10.0.0.0/24 ] destination [ any ] service [ any ] to-interface [ ethernet1/2 ] snat-interface
show session all filter source 10.0.0.5
session id 12345, application incomplete, source 10.0.0.5:50000, destination 203.0.113.1:80, nat source 10.0.0.5, nat destination 203.0.113.1, rule Allow-Web, nat rule NAT-Internet, state active, type flow
Refer to the exhibit. A user from the trust zone (10.0.0.5) is trying to access a web server at 203.0.113.1 on port 80. The firewall shows a session with application 'incomplete'. What is the most likely reason for this?
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.
Refer to the exhibit.
show system info | match model
vm-series
show running security-policy
set rulebase security rules "Allow-Web" from [ trust ] to [ untrust ] source [ 10.0.0.0/24 ] destination [ any ] application [ web-browsing ] service [ application-default ] action allow
set rulebase security rules "Block-All" from [ any ] to [ any ] source [ any ] destination [ any ] application [ any ] service [ any ] action deny
show running nat-policy
set rulebase nat rules "NAT-Internet" from [ trust ] to [ untrust ] source [ 10.0.0.0/24 ] destination [ any ] service [ any ] to-interface [ ethernet1/2 ] snat-interface
show session all filter source 10.0.0.5
session id 12345, application incomplete, source 10.0.0.5:50000, destination 203.0.113.1:80, nat source 10.0.0.5, nat destination 203.0.113.1, rule Allow-Web, nat rule NAT-Internet, state active, type flow
A
The traffic is not matching the application 'web-browsing'
The session has application 'incomplete', indicating the firewall has not identified the application as 'web-browsing', so the traffic is denied by the implicit deny.
B
The NAT rule is missing
Why wrong: The session shows a NAT rule 'NAT-Internet' applied, so NAT is not missing.
C
The destination IP is not in the destination zone
Why wrong: The destination is 'any' in the rule, so zone matching is not an issue.
D
The security rule 'Allow-Web' is configured after 'Block-All'
Why wrong: The running config shows 'Allow-Web' first, so rule order is correct.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The traffic is not matching the application 'web-browsing'
The session shows application 'incomplete' because the firewall has not yet identified the application due to insufficient data or because the traffic does not match the expected application signature. In this case, the traffic is likely not matching the 'web-browsing' application, which is the application defined in the security rule 'Allow-Web'. The firewall requires the first few packets to complete application identification; if the traffic is not recognized as 'web-browsing' (e.g., due to non-standard HTTP headers or encrypted payloads), the session remains 'incomplete' and may be dropped or not allowed by the rule.
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.
✓
The traffic is not matching the application 'web-browsing'
Why this is correct
The session has application 'incomplete', indicating the firewall has not identified the application as 'web-browsing', so the traffic is denied by the implicit deny.
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.
✗
The NAT rule is missing
Why it's wrong here
The session shows a NAT rule 'NAT-Internet' applied, so NAT is not missing.
✗
The destination IP is not in the destination zone
Why it's wrong here
The destination is 'any' in the rule, so zone matching is not an issue.
✗
The security rule 'Allow-Web' is configured after 'Block-All'
Why it's wrong here
The running config shows 'Allow-Web' first, so rule order is correct.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'incomplete' application state with a missing security rule or NAT issue, but the 'incomplete' state specifically indicates that the firewall has not yet identified the application, not that the traffic is blocked or unroutable.
Trap categories for this question
Command / output trap
The session shows a NAT rule 'NAT-Internet' applied, so NAT is not missing.
Detailed technical explanation
How to think about this question
The 'incomplete' application state in Palo Alto Networks firewalls indicates that the firewall has not yet completed application identification, which typically occurs when the traffic does not match the expected application signature within the first few packets (e.g., the first 4-8 packets for HTTP). This can happen if the traffic uses non-standard ports, custom HTTP headers, or encrypted payloads that prevent the firewall from matching the 'web-browsing' application. In real-world scenarios, this often occurs with applications that use HTTP but with non-standard methods or content, causing the firewall to keep the session in 'incomplete' until timeout or until more data is received.
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.
Palo Alto Networks Platforms and Architecture — This question tests Palo Alto Networks Platforms and Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The traffic is not matching the application 'web-browsing' — The session shows application 'incomplete' because the firewall has not yet identified the application due to insufficient data or because the traffic does not match the expected application signature. In this case, the traffic is likely not matching the 'web-browsing' application, which is the application defined in the security rule 'Allow-Web'. The firewall requires the first few packets to complete application identification; if the traffic is not recognized as 'web-browsing' (e.g., due to non-standard HTTP headers or encrypted payloads), the session remains 'incomplete' and may be dropped or not allowed by the rule.
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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