This CV0-004 practice question tests your understanding of troubleshooting. 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.
Network Topology
The exhibit shows the health check status for targets in an application load balancer's target group. The target group has a health check on port 80. An administrator notices that one target is unhealthy on port 80 but healthy on port 443. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group for the target is blocking port 80 from the load balancer.
Option A is correct because the target is healthy on 443 but not on 80, suggesting port 80 is blocked. Option B is wrong because it's healthy on 443, so server is listening. Option C is wrong because if path were wrong, both would fail. Option D is wrong because the same target group is used.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 web server on the target is not listening on port 443.
Why it's wrong here
The target is healthy on port 443, so the web server is listening.
✓
The security group for the target is blocking port 80 from the load balancer.
Why this is correct
A security group blocking port 80 would cause the health check on port 80 to fail, while port 443 remains healthy.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The load balancer is in a different VPC.
Why it's wrong here
Same target group implies same VPC.
✗
The health check path is incorrect.
Why it's wrong here
An incorrect path would affect both ports if the same path is used, but the health check is on different ports.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CV0-004 NAT questions on configuration and troubleshooting.
Troubleshooting — This question tests Troubleshooting — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The security group for the target is blocking port 80 from the load balancer. — Option A is correct because the target is healthy on 443 but not on 80, suggesting port 80 is blocked. Option B is wrong because it's healthy on 443, so server is listening. Option C is wrong because if path were wrong, both would fail. Option D is wrong because the same target group is used.
What should I do if I get this CV0-004 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CV0-004 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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