- A
The firewall will automatically redistribute the route to VR-B if needed.
Why wrong: Redistribution must be configured explicitly; it is not automatic.
- B
The firewall will perform a reverse path forwarding (RPF) check on the source IP.
RPF ensures the source IP is reachable via the incoming interface; if not, the packet may be dropped.
- C
The packet will be dropped because the destination is not in the same VR as the ingress interface.
Why wrong: The destination is in VR-A, which matches the ingress interface's VR.
- D
The firewall will use the zone of the egress interface to determine the security policy.
Why wrong: Policy lookup uses ingress and egress zones; the egress zone is based on the route, but the statement is true in general, however the question asks about the forwarding decision specifically.
Quick Answer
The answer is that the firewall will perform a reverse path forwarding (RPF) check on the source IP. This occurs because after a successful route lookup in VR-A, the Palo Alto Networks firewall enforces an RPF check to verify that the source address of the incoming packet is reachable via the same ingress interface, a critical anti-spoofing mechanism. Since the interface belongs to VR-A and the route to 10.0.0.0/8 exists there, the firewall checks that the source IP’s return path matches the ingress interface; if not, the packet is dropped. On the PCNSE exam, this concept tests your understanding of how virtual routers enforce unicast RPF independently per routing table, a common trap being that RPF is often confused with route lookup order. Remember the mnemonic: “Route first, then reverse—if the source can’t return, the packet will burn.”
PCNSE Core Concepts and Architecture Practice Question
This PCNSE practice question tests your understanding of core concepts and architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 Palo Alto Networks firewall is configured with two virtual routers: VR-A (trust) and VR-B (untrust). An interface is placed in VR-A. A static route to 10.0.0.0/8 via next-hop 192.168.1.1 exists in VR-A. The firewall receives a packet from the trust zone destined to 10.1.1.1. The route lookup succeeds in VR-A. Which statement is true about the forwarding decision?
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
The firewall will perform a reverse path forwarding (RPF) check on the source IP.
Option B is correct because when a packet enters a Palo Alto Networks firewall, after a successful route lookup, the firewall performs an RPF check on the source IP address to ensure that the source is reachable via the ingress interface. This is a fundamental security mechanism to prevent spoofed traffic. Since the ingress interface is in VR-A and the route lookup succeeded, the RPF check verifies that the source IP of the packet is reachable through that same interface; if not, the packet is dropped.
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 will automatically redistribute the route to VR-B if needed.
Why it's wrong here
Redistribution must be configured explicitly; it is not automatic.
- ✓
The firewall will perform a reverse path forwarding (RPF) check on the source IP.
Why this is correct
RPF ensures the source IP is reachable via the incoming interface; if not, the packet may be dropped.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The packet will be dropped because the destination is not in the same VR as the ingress interface.
Why it's wrong here
The destination is in VR-A, which matches the ingress interface's VR.
- ✗
The firewall will use the zone of the egress interface to determine the security policy.
Why it's wrong here
Policy lookup uses ingress and egress zones; the egress zone is based on the route, but the statement is true in general, however the question asks about the forwarding decision specifically.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the packet will be dropped because the destination is in a different VR (Option C), but they overlook that the route lookup succeeded in the ingress VR, meaning the egress interface is within the same VR, and the real security mechanism is the RPF check on the source IP.
Detailed technical explanation
How to think about this question
The RPF check in Palo Alto Networks is performed by default on all ingress traffic and uses the FIB (Forwarding Information Base) of the virtual router to verify that the source IP is reachable via the ingress interface. If the source IP is not in the routing table or is reachable via a different interface, the packet is silently dropped. This behavior is similar to unicast RPF (uRPF) in strict mode on Cisco devices, but it is always enabled and cannot be disabled on PAN-OS. In a multi-VR scenario, the RPF check is scoped to the VR of the ingress interface, so a source IP that is only reachable via VR-B would fail the check if the packet enters via VR-A.
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.
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FAQ
Questions learners often ask
What does this PCNSE question test?
Core Concepts and Architecture — This question tests Core Concepts and Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The firewall will perform a reverse path forwarding (RPF) check on the source IP. — Option B is correct because when a packet enters a Palo Alto Networks firewall, after a successful route lookup, the firewall performs an RPF check on the source IP address to ensure that the source is reachable via the ingress interface. This is a fundamental security mechanism to prevent spoofed traffic. Since the ingress interface is in VR-A and the route lookup succeeded, the RPF check verifies that the source IP of the packet is reachable through that same interface; if not, the packet is dropped.
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.
About these practice questions
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 →
Last reviewed: Jun 11, 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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