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CV0-004 Practice Question: Refer to the exhibit
Network Topology
Refer to the exhibit. A cloud administrator is troubleshooting why an EC2 instance in subnet-12345678 cannot be reached from the internet. The instance has a public IP and the security group allows all inbound traffic. Based on the exhibit, what is the most likely cause?
⚠ Common exam trap
A common trap is that candidates assume a permissive security group is sufficient, overlooking the NACL's explicit deny rule that blocks all traffic at the subnet boundary.
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 network ACL is misconfigured and blocking all inbound traffic.
The exhibit shows that the network ACL (NACL) associated with subnet-12345678 has an inbound rule that denies all traffic (rule number 100 with DENY for 0.0.0.0/0). Since NACLs are stateless and evaluated in order, this explicit deny overrides any allow rules, blocking all inbound internet traffic to the EC2 instance regardless of the security group settings or the instance having a public IP.
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 security group is not applied.
Why it's wrong here
The exhibit does not show security group association; the problem states the security group allows all inbound, so it is likely applied.
- ✗
The route table is missing a default route to the internet gateway.
Why it's wrong here
The exhibit does not show route tables; it shows a network ACL with a deny rule.
- ✗
The instance is stopped.
Why it's wrong here
The exhibit does not show instance state; the problem statement says the instance has a public IP, implying it is running.
- ✓
The network ACL is misconfigured and blocking all inbound traffic.
Why this is correct
The network ACL has a deny rule for all inbound traffic, which overrides the security group's allow.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.