PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing 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 company has a VPC with the above firewall rule applied. They have a VM instance with network tag 'web-server' that hosts a web server. Users report they cannot access the web server from the internet. What is the most likely cause?
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 targetTags filter is incorrectly spelled; it should be 'webserver' instead of 'web-server'.
Why wrong: The exhibit shows 'web-server' which matches the VM's tag, so spelling is correct.
B
The firewall rule is disabled.
Why wrong: The exhibit shows disabled: false, meaning the rule is enabled.
C
The VM instance does not have a public IP address.
Without a public IP, the VM cannot be reached from the internet.
D
The firewall rule priority is too high (1000), causing it to be overridden by a deny rule with lower priority.
Why wrong: Priority 1000 is the default; lower numbers have higher priority, so a deny rule with lower priority number could override, but this is not the most likely cause without evidence.
E
The firewall rule does not allow traffic from the internet because sourceRanges is set to 0.0.0.0/0.
Why wrong: sourceRanges 0.0.0.0/0 actually allows all source IPs, including the internet.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VM instance does not have a public IP address.
Option B is correct because a VM without a public IP address cannot receive traffic from the internet, regardless of firewall rules. Option A is incorrect because sourceRanges 0.0.0.0/0 allows all sources. Option C is incorrect because priority 1000 is default and not necessarily overridden by a higher priority deny rule. Option D is incorrect because the targetTags filter matches the VM's tag. Option E is incorrect because the rule is not disabled.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 targetTags filter is incorrectly spelled; it should be 'webserver' instead of 'web-server'.
Why it's wrong here
The exhibit shows 'web-server' which matches the VM's tag, so spelling is correct.
✗
The firewall rule is disabled.
Why it's wrong here
The exhibit shows disabled: false, meaning the rule is enabled.
✓
The VM instance does not have a public IP address.
Why this is correct
Without a public IP, the VM cannot be reached from the internet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The firewall rule priority is too high (1000), causing it to be overridden by a deny rule with lower priority.
Why it's wrong here
Priority 1000 is the default; lower numbers have higher priority, so a deny rule with lower priority number could override, but this is not the most likely cause without evidence.
✗
The firewall rule does not allow traffic from the internet because sourceRanges is set to 0.0.0.0/0.
Why it's wrong here
sourceRanges 0.0.0.0/0 actually allows all source IPs, including the internet.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
The exhibit shows 'web-server' which matches the VM's tag, so spelling is correct.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNE ACL questions on filtering logic and placement.
Implementing network security — This question tests Implementing network security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The VM instance does not have a public IP address. — Option B is correct because a VM without a public IP address cannot receive traffic from the internet, regardless of firewall rules. Option A is incorrect because sourceRanges 0.0.0.0/0 allows all sources. Option C is incorrect because priority 1000 is default and not necessarily overridden by a higher priority deny rule. Option D is incorrect because the targetTags filter matches the VM's tag. Option E is incorrect because the rule is not disabled.
What should I do if I get this PCNE question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNE ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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Question Discussion
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