The answer is that the Allow_SSH policy has tunnel detection set to none, so it fails to match SSH tunnels. This is because Palo Alto Networks firewalls rely on tunnel detection attributes within application policies to identify and permit encapsulated traffic like SSH tunnels; when tunnel detection is disabled, the firewall cannot recognize the SSH tunnel as matching the policy, causing it to be blocked by default. On the PCNSA exam, this concept tests your understanding of how application-based policies interact with tunnel detection settings, often appearing as a trick where a seemingly permissive SSH rule is bypassed due to missing detection parameters. A common trap is assuming any SSH policy will allow all SSH traffic, but without tunnel detection, the firewall treats the tunnel as unknown traffic. Remember: no detection, no match—think of it as the firewall needing its “tunnel vision” turned on to see the tunnel.
PCNSA Securing Traffic Practice Question
This PCNSA practice question tests your understanding of securing traffic. 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.
Exhibit
Refer to the exhibit.
Exhibit: Config snippet:
```
set shared application-tunnel time-to-live 30
set shared application-tunnel policy "Block_Tor" action deny
set shared application-tunnel policy "Allow_SSH" action allow tunnel detection none
```
An administrator notices that SSH tunnels are being blocked by the firewall. According to the exhibit, what is the most likely cause?
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.
Exhibit: Config snippet:
```
set shared application-tunnel time-to-live 30
set shared application-tunnel policy "Block_Tor" action deny
set shared application-tunnel policy "Allow_SSH" action allow tunnel detection none
```
A
The policy "Allow_SSH" has tunnel detection set to none, so it does not match.
Without tunnel detection, the firewall cannot identify SSH tunnels, so the Allow_SSH policy never applies, and tunnels are likely blocked by the default or other rules.
B
The application tunnel policy "Block_Tor" is blocking all tunnels.
Why wrong: Block_Tor specifically blocks Tor tunnels, not SSH.
C
The time-to-live setting prevents SSH tunnel detection.
Why wrong: TTL is not related to detection; it's for session timeouts.
D
The default action for application tunnels is deny.
Why wrong: The exhibit shows explicit policies; default action is not shown and typically is allow? Actually, for application tunnels, if no policy matches, the default is to allow? But the issue is that SSH tunnel is not being detected, not that it's denied by default.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The policy "Allow_SSH" has tunnel detection set to none, so it does not match.
Option D is correct because tunnel detection set to 'none' on the Allow_SSH policy means the firewall does not detect SSH tunnels, so they are not allowed. The default behavior for application tunnels is to check tunnel detection attributes; without detection, the tunnel policy does not match. Option A is wrong because Block_Tor only blocks Tor. Option B is not necessarily default. Option C is not relevant.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 policy "Allow_SSH" has tunnel detection set to none, so it does not match.
Why this is correct
Without tunnel detection, the firewall cannot identify SSH tunnels, so the Allow_SSH policy never applies, and tunnels are likely blocked by the default or other rules.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The application tunnel policy "Block_Tor" is blocking all tunnels.
Why it's wrong here
Block_Tor specifically blocks Tor tunnels, not SSH.
✗
The time-to-live setting prevents SSH tunnel detection.
Why it's wrong here
TTL is not related to detection; it's for session timeouts.
✗
The default action for application tunnels is deny.
Why it's wrong here
The exhibit shows explicit policies; default action is not shown and typically is allow? Actually, for application tunnels, if no policy matches, the default is to allow? But the issue is that SSH tunnel is not being detected, not that it's denied by default.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
The exhibit shows explicit policies; default action is not shown and typically is allow? Actually, for application tunnels, if no policy matches, the default is to allow? But the issue is that SSH tunnel is not being detected, not that it's denied by default.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNSA ACL questions on filtering logic and placement.
Securing Traffic — This question tests Securing Traffic — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The policy "Allow_SSH" has tunnel detection set to none, so it does not match. — Option D is correct because tunnel detection set to 'none' on the Allow_SSH policy means the firewall does not detect SSH tunnels, so they are not allowed. The default behavior for application tunnels is to check tunnel detection attributes; without detection, the tunnel policy does not match. Option A is wrong because Block_Tor only blocks Tor. Option B is not necessarily default. Option C is not relevant.
What should I do if I get this PCNSA question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNSA ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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