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CV0-004 Practice Question: A cloud administrator is troubleshooting a…
A cloud administrator is troubleshooting a connectivity issue between a web server and a database server in the same VPC but different subnets. The security group for the database server allows inbound traffic from the web server's security group. However, the web server cannot establish a TCP connection to the database. What are two possible causes? (Choose two.)
⚠ Common exam trap
Candidates often assume security groups are the only firewall layer, forgetting that network ACLs at the subnet level can override security group rules, especially when they are stateless and require explicit rules for both directions.
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 of the web server subnet is blocking outbound traffic.
Network ACLs are stateless and apply to subnet boundaries. Even if the web server's security group allows outbound traffic, the subnet's network ACL must explicitly allow outbound traffic to the database server's IP and port. If the outbound rule is missing or denies the traffic, the TCP SYN packet will be dropped before it leaves the subnet. Option C is correct because the database subnet's network ACL must allow inbound traffic from the web server's IP and port; if it blocks the inbound SYN, the connection cannot be established.
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 of the web server does not allow outbound traffic to the database.
Why it's wrong here
Default security groups allow all outbound traffic; unless modified, this is unlikely.
- ✓
The network ACL of the web server subnet is blocking outbound traffic.
Why this is correct
The outbound NACL on the web server subnet may block the connection request.
- ✓
The network ACL of the database subnet is blocking inbound traffic.
Why this is correct
The inbound NACL on the database subnet may deny traffic, overriding the security group allow.
- ✗
The route table of the database subnet does not contain a route to the web server subnet.
Why it's wrong here
VPC automatically adds a local route, so route tables are not an issue.
- ✗
The database server is not listening on the correct port.
Why it's wrong here
This is an application-level issue, not a network connectivity issue.
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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.