CV0-004 Troubleshooting Practice Question
Exhibit
Refer to the exhibit. VPC Flow Logs excerpt: 2 123456789010 eni-12345678 10.0.1.5 10.0.2.10 12345 80 6 1500 100 1625082000 1625082060 ACCEPT OK 2 123456789010 eni-12345678 10.0.1.5 10.0.2.10 12346 80 6 1500 200 1625082061 1625082121 ACCEPT OK 2 123456789010 eni-12345678 10.0.1.5 10.0.2.10 12347 80 6 100 0 1625082122 1625082182 REJECT OK
The exhibit shows VPC flow log entries for an EC2 instance (eni-12345678). The administrator is troubleshooting a connectivity problem where an application on 10.0.1.5 occasionally cannot connect to a web server at 10.0.2.10 on port 80. What action should the administrator take?
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
✓
Add a network ACL rule allowing inbound TCP/80 from 10.0.1.5 to the subnet of 10.0.2.10.
The REJECT entry in the VPC flow log indicates that traffic is being blocked by a network ACL (NACL), which is stateless. Security groups are stateful and do not produce REJECT entries; they either allow or silently drop traffic. To resolve the issue, the administrator must add an inbound rule to the network ACL associated with the subnet of the web server (10.0.2.10) to allow TCP port 80 from the source IP 10.0.1.5. Option C is correct. Option A is incorrect because increasing the MTU does not affect firewall blocking. Option B is incorrect because a security group rule would not generate a REJECT; the REJECT indicates a NACL blockage. Option D is incorrect because adding a route does not address firewall filtering.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the MTU on the instance to 9001.
Why it's wrong here
MTU issues would cause different symptoms, not REJECT.
- ✗
Add a security group rule allowing inbound TCP/80 from 10.0.1.5.
Why it's wrong here
Security groups are stateful and allow return traffic; the REJECT in flow logs indicates a NACL, not a security group.
- ✓
Add a network ACL rule allowing inbound TCP/80 from 10.0.1.5 to the subnet of 10.0.2.10.
Why this is correct
NACLs are stateless and require explicit inbound rules; the REJECT indicates a NACL block.
- ✗
Add a route to the VPC route table for 10.0.1.5.
Why it's wrong here
Routes determine the path, not filtering; the flow logs show traffic reaching the target, so routing is fine.
Visual reference
Go deeper
Related to this question
About these practice questions
This CV0-004 question is part of Courseiva's 977-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.