Question 1,651 of 1,621
ANS-C01 Network Design Practice Question
A company has a VPC with a CIDR of 172.16.0.0/16. They have a subnet 172.16.1.0/24 for web servers and another subnet 172.16.2.0/24 for database servers. The web servers need to access the database servers on port 3306. Which configuration is required?
⚠ Common exam trap
It's easy for candidates to confuse the stateless nature of network ACLs with the stateful behavior of security groups, or they incorrectly assume that inbound rules on the source security group are needed instead of outbound rules on the source and inbound rules on the destination.
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
✓
Web SG: outbound to DB SG on port 3306. DB SG: inbound from web SG on port 3306.
Security groups are stateful and control traffic at the instance level. The web server security group needs an outbound rule allowing traffic to the database security group on port 3306, and the database security group needs an inbound rule allowing traffic from the web security group on port 3306. This ensures that only the web servers can initiate connections to the database servers on the required port.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure network ACLs to allow inbound on port 3306 from web subnet.
Why it's wrong here
Configuring network ACLs solely for inbound port 3306 is insufficient because network ACLs are stateless. They require explicit outbound rules for return traffic on ephemeral ports to allow the database server's response to reach the web server. This option is tempting as ACLs do control traffic at the subnet level, providing a coarse-grained security layer. They would be appropriate for blocking specific IP ranges, or as an additional, stateless firewall for entire subnets, but not as the complete solution for instance-to-instance communication.
- ✗
Web SG: inbound from 0.0.0.0/0 on port 3306. DB SG: outbound to web SG on port 3306.
Why it's wrong here
Inbound on web is unnecessary.
- ✓
Web SG: outbound to DB SG on port 3306. DB SG: inbound from web SG on port 3306.
Why this is correct
Allows only MySQL traffic from web to DB.
- ✗
Web SG: outbound to DB SG on all ports. DB SG: inbound from web SG on all ports.
Why it's wrong here
Allows all protocols, not least privilege.
Visual reference
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Last reviewed: Jun 24, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.
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