The answer is a missing ACL to match the traffic to be translated. Without an access control list applied to the NAT rule, the firewall has no criteria to identify which source IP addresses—such as those from VLAN 10—should undergo translation, so packets are forwarded without NAT and dropped by the ISP router. On the Cisco SCOR / CCNP Security Core 350-701 exam, this scenario tests your understanding that NAT configuration requires both a translation rule and a matching ACL; a common trap is assuming a default route alone enables translation. Remember the memory tip: “No ACL, no match—NAT won’t catch.”
350-701 Network Security Practice Question
This 350-701 practice question tests your understanding of network security. 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 network engineer is troubleshooting an issue where users on VLAN 10 cannot access the internet, but they can reach internal resources. The firewall is configured with a default route pointing to the ISP router. The engineer notices that NAT is configured but traffic is not being translated. Which configuration is most likely missing?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An ACL to match the traffic to be translated
For NAT to translate traffic, the firewall must know which traffic to translate. An ACL is used to match the source IP addresses (or networks) that should be translated. Without an ACL applied to the NAT rule, the firewall has no criteria to identify traffic from VLAN 10 for translation, so packets are forwarded without NAT, causing internet access to fail while internal routing works.
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.
✓
An ACL to match the traffic to be translated
Why this is correct
The ACL defines interesting traffic for NAT; without it, no packets are matched for translation.
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.
✗
A NAT pool with available public IP addresses
Why it's wrong here
A NAT pool is needed for dynamic NAT, but the immediate issue is the missing ACL to match traffic.
✗
Port Address Translation (PAT) configuration
Why it's wrong here
PAT is a type of NAT, but the missing element is the ACL to identify traffic for translation.
✗
A route map to apply NAT based on destination
Why it's wrong here
Route maps are optional for policy-based NAT; standard NAT requires an ACL first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply enabling NAT or PAT is enough, but the ACL is the critical component that defines the traffic to be translated, and candidates may overlook it because they assume NAT applies to all traffic by default.
Detailed technical explanation
How to think about this question
In Cisco IOS and ASA firewalls, NAT configuration typically uses the command 'ip nat inside source list <ACL> interface <outside> overload' for PAT. The ACL defines the 'interesting traffic' that triggers translation. Without this ACL, the NAT process has no match condition, so packets bypass translation even if NAT is enabled. A common real-world scenario is when a network has multiple VLANs and only one VLAN needs internet access; the ACL must specifically permit that VLAN's subnet.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An ACL to match the traffic to be translated — For NAT to translate traffic, the firewall must know which traffic to translate. An ACL is used to match the source IP addresses (or networks) that should be translated. Without an ACL applied to the NAT rule, the firewall has no criteria to identify traffic from VLAN 10 for translation, so packets are forwarded without NAT, causing internet access to fail while internal routing works.
What should I do if I get this 350-701 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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