PCNSE Deploy and Configure Firewalls Practice Question
This PCNSE practice question tests your understanding of deploy and configure firewalls. 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.
A security engineer is deploying a new PA-5220 firewall to replace an existing legacy firewall. The environment has complex routing with OSPF and BGP. The engineer configures the firewall with multiple virtual routers: one for the internal network, one for the DMZ, and one for the external connection to two ISPs. The firewall is placed in Layer 3 mode. After the cutover, users report that they can access the internet but internal traffic between two different subnets that are both in the internal virtual router fails to route properly. The engineer checks the routing table on the internal virtual router and sees correct OSPF learned routes. The security policies allow all traffic between those subnets. What is the most likely cause of the routing failure?
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.
The firewall does not have a loopback interface for OSPF router-id
Why wrong: OSPF router-id can be set manually; loopback is not mandatory.
B
The security policy is not correctly identifying the traffic due to asymmetric routing
Why wrong: Asymmetric routing is possible but less likely; the issue is routing, not policy match.
C
The internal interfaces are assigned to different virtual routers
If the interfaces belong to different virtual routers, the firewall will not route between them by default without inter-VR route leaking or a shared VR.
D
The OSPF metric is too high, causing route preference issues
Why wrong: Routes are present in the routing table; OSPF metric affects path selection, not reachability.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The internal interfaces are assigned to different virtual routers
The most likely cause is that the internal interfaces are assigned to different virtual routers. In a Palo Alto Networks firewall, Layer 3 interfaces belong to a specific virtual router, and routing between subnets in different virtual routers requires either a route leak or a shared virtual router. Since the engineer placed both subnets in the same internal virtual router but the interfaces are in different virtual routers, the firewall cannot route traffic between them even if the routing table and security policies are correct.
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 firewall does not have a loopback interface for OSPF router-id
Why it's wrong here
OSPF router-id can be set manually; loopback is not mandatory.
✗
The security policy is not correctly identifying the traffic due to asymmetric routing
Why it's wrong here
Asymmetric routing is possible but less likely; the issue is routing, not policy match.
✓
The internal interfaces are assigned to different virtual routers
Why this is correct
If the interfaces belong to different virtual routers, the firewall will not route between them by default without inter-VR route leaking or a shared VR.
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 OSPF metric is too high, causing route preference issues
Why it's wrong here
Routes are present in the routing table; OSPFmetric affects path selection, not reachability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume that security policies alone control traffic flow, forgetting that virtual routers create isolated routing domains, and that interfaces in different virtual routers cannot route to each other without explicit route leaking or redistribution.
Detailed technical explanation
How to think about this question
Palo Alto Networks firewalls use virtual routers to maintain separate routing tables and forwarding decisions. When interfaces are in different virtual routers, the firewall does not perform inter-virtual-router routing by default; traffic must be explicitly leaked using redistribution or by placing all relevant interfaces in the same virtual router. In this scenario, the engineer created multiple virtual routers for segmentation, but the internal subnets must share a single virtual router to route directly between them without additional configuration.
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 at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
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.
Deploy and Configure Firewalls — This question tests Deploy and Configure Firewalls — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The internal interfaces are assigned to different virtual routers — The most likely cause is that the internal interfaces are assigned to different virtual routers. In a Palo Alto Networks firewall, Layer 3 interfaces belong to a specific virtual router, and routing between subnets in different virtual routers requires either a route leak or a shared virtual router. Since the engineer placed both subnets in the same internal virtual router but the interfaces are in different virtual routers, the firewall cannot route traffic between them even if the routing table and security policies are correct.
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.
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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