The answer is the route 10.0.0.0/24 via 10.0.0.2 ethernet1/2, because the Palo Alto firewall applies the longest prefix match algorithm to determine the most specific route for forwarding. When a packet with destination IP 10.0.0.100 arrives, the firewall compares it against all routing table entries; the /24 subnet matches 256 addresses including .100, while the /8 subnet covers a much broader range, and the default route is the least specific. On the PCNSE exam, this concept tests your understanding of how the firewall processes routing decisions before security policies, and a common trap is assuming the default route or a larger subnet is chosen first—remember that longer prefix lengths always win. A helpful memory tip is “the more bits, the better fit,” meaning the route with the highest subnet mask number (e.g., /24 over /8) is always preferred.
PCNSE Core Concepts and Architecture Practice Question
This PCNSE practice question tests your understanding of core concepts 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.
```
admin@PA-5050> show routing route
IPv4 Virtual Router: default
destination nexthop interface metric flags
0.0.0.0/0 10.0.0.1 ethernet1/1 10 A S
10.0.0.0/8 10.0.0.1 ethernet1/1 10 A S
10.0.0.0/24 10.0.0.2 ethernet1/2 10 A S
10.0.1.0/24 10.0.0.3 ethernet1/3 10 A S
172.16.0.0/12 10.0.0.4 ethernet1/4 10 A S
192.168.0.0/16 10.0.0.5 ethernet1/5 10 A S
```
A firewall has the routing table shown. A packet arrives on ethernet1/2 with source IP 10.0.0.50 and destination IP 10.0.0.100. Which route will be used for forwarding?
Refer to the exhibit.
```
admin@PA-5050> show routing route
IPv4 Virtual Router: default
destination nexthop interface metric flags
0.0.0.0/0 10.0.0.1 ethernet1/1 10 A S
10.0.0.0/8 10.0.0.1 ethernet1/1 10 A S
10.0.0.0/24 10.0.0.2 ethernet1/2 10 A S
10.0.1.0/24 10.0.0.3 ethernet1/3 10 A S
172.16.0.0/12 10.0.0.4 ethernet1/4 10 A S
192.168.0.0/16 10.0.0.5 ethernet1/5 10 A S
```
A
10.0.0.0/24 via 10.0.0.2 ethernet1/2
Longest prefix match: /24 is more specific than /8.
B
10.0.1.0/24 via 10.0.0.3 ethernet1/3
Why wrong: Destination 10.0.0.100 is not in 10.0.1.0/24.
C
10.0.0.0/8 via 10.0.0.1 ethernet1/1
Why wrong: The /8 route is less specific than the /24 route.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
10.0.0.0/24 via 10.0.0.2 ethernet1/2
The firewall performs a longest-prefix match on the routing table. The destination IP 10.0.0.100 matches the 10.0.0.0/24 route (prefix length 24) more specifically than the 10.0.0.0/8 route (prefix length 8) or the default route. Since the packet arrived on ethernet1/2 and the matching route points to the same interface, the route via 10.0.0.2 ethernet1/2 is selected.
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.
✓
10.0.0.0/24 via 10.0.0.2 ethernet1/2
Why this is correct
Longest prefix match: /24 is more specific than /8.
Related concept
Read the scenario before looking for a memorised answer.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often pick the default route or the classful /8 route without considering the longest-prefix match rule, mistakenly assuming that a broader match or the default route is sufficient for forwarding.
Detailed technical explanation
How to think about this question
The longest-prefix match algorithm is fundamental to IP forwarding: the router compares the destination IP against all routes and selects the one with the most specific (longest) subnet mask. In this scenario, the /24 route is chosen over the /8 route even though both match, because the /24 provides a more precise match. This behavior is defined in RFC 1812 and is implemented in all routing protocols and forwarding engines, including PAN-OS.
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.
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: 10.0.0.0/24 via 10.0.0.2 ethernet1/2 — The firewall performs a longest-prefix match on the routing table. The destination IP 10.0.0.100 matches the 10.0.0.0/24 route (prefix length 24) more specifically than the 10.0.0.0/8 route (prefix length 8) or the default route. Since the packet arrived on ethernet1/2 and the matching route points to the same interface, the route via 10.0.0.2 ethernet1/2 is selected.
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 →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.