- A
Verify the routing table on both firewalls.
Correct. Routing must direct traffic into the tunnel.
- B
Check the firewall policies for the tunnel zone.
Correct. Security policies must allow traffic through the tunnel interface.
- C
Increase the IPSec SA lifetime.
Why wrong: Incorrect. Lifetime does not affect whether traffic passes; it controls renegotiation.
- D
Verify the proxy IDs on both peers match.
Correct. Mismatched proxy IDs prevent traffic from being encrypted.
- E
Ensure the tunnel interface is placed in a virtual router.
Why wrong: Incorrect. The tunnel interface is implicitly routed; placement is not required for basic connectivity.
Question 279 of 516
Site-to-Site VPN Tunnel Is Up But No Traffic Passes: Troubleshooting Steps
This PCNSE practice question tests your understanding of secure access and vpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 THREE troubleshooting steps should be taken when a site-to-site VPN tunnel is up but no traffic passes?
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
✓
Verify the routing table on both firewalls.
Option A is correct because even if the VPN tunnel is up (Phase 1 and Phase 2 SAs established), traffic may still fail if the firewall does not have a route to the destination network via the tunnel interface. Without a correct route in the routing table, the firewall will drop the packet or send it out the wrong interface. Verifying the routing table ensures that the tunnel interface is the next hop for the remote subnet.
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.
- ✓
Verify the routing table on both firewalls.
Why this is correct
Correct. Routing must direct traffic into the tunnel.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Check the firewall policies for the tunnel zone.
Why this is correct
Correct. Security policies must allow traffic through the tunnel interface.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the IPSec SA lifetime.
Why it's wrong here
Incorrect. Lifetime does not affect whether traffic passes; it controls renegotiation.
- ✓
Verify the proxy IDs on both peers match.
Why this is correct
Correct. Mismatched proxy IDs prevent traffic from being encrypted.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Ensure the tunnel interface is placed in a virtual router.
Why it's wrong here
Incorrect. The tunnel interface is implicitly routed; placement is not required for basic connectivity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a tunnel being 'up' guarantees traffic flow, but the PCNSE exam tests that you must separately verify routing, security policies, and proxy IDs—each of which can block traffic independently of the tunnel's control-plane state.
Detailed technical explanation
How to think about this question
When a site-to-site VPN tunnel is up but no traffic passes, the most common causes are missing routes (e.g., no static route pointing to the tunnel interface) or security policies that do not allow traffic from the source zone to the tunnel zone. Additionally, proxy IDs (IPSec security associations) must match exactly on both peers; a mismatch can cause the tunnel to establish but silently drop traffic because the encryption domain does not align. In Palo Alto Networks firewalls, the tunnel interface must be assigned to a virtual router and the correct zone, and policies must explicitly permit traffic between the source and destination zones.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Visual reference
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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Secure Access and VPN — study guide chapter
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FAQ
Questions learners often ask
What does this PCNSE question test?
Secure Access and VPN — This question tests Secure Access and VPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Verify the routing table on both firewalls. — Option A is correct because even if the VPN tunnel is up (Phase 1 and Phase 2 SAs established), traffic may still fail if the firewall does not have a route to the destination network via the tunnel interface. Without a correct route in the routing table, the firewall will drop the packet or send it out the wrong interface. Verifying the routing table ensures that the tunnel interface is the next hop for the remote subnet.
What should I do if I get this PCNSE 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.
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Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jul 4, 2026
This PCNSE practice question is part of Courseiva's free Palo Alto Networks 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 PCNSE exam.
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