Question 28 of 1,621
ANS-C01 Network Implementation Practice Question
A network engineer is troubleshooting connectivity issues between an on-premises network and a VPC over a Direct Connect private VIF. The on-premises network can reach EC2 instances in the VPC, but cannot reach an RDS database in the same VPC. The VPC has a single subnet. What is the MOST likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the distinction between security groups and network ACLs, and the trap here is that candidates assume a subnet-level ACL (Option A) is the cause when the symptom is specific to one resource type, overlooking that security groups operate at the instance level and can selectively block traffic.
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 RDS database security group is not allowing inbound traffic from the on-premises CIDR
Since the on-premises network can reach EC2 instances but not the RDS database, the issue is likely at the security group level, not the network ACL or routing. Security groups are stateful and act as a virtual firewall for instances; by default, they deny all inbound traffic unless explicitly allowed. The RDS database's security group must have an inbound rule permitting traffic from the on-premises CIDR range, and its absence would block the connection while leaving EC2 access unaffected.
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 VPC network ACL is blocking inbound traffic from on-premises
Why it's wrong here
Possible but less likely than security group; NACLs are stateless.
- ✗
The direct connect virtual interface is configured for a different VLAN
Why it's wrong here
Would affect all traffic, not just RDS.
- ✓
The RDS database security group is not allowing inbound traffic from the on-premises CIDR
Why this is correct
Security groups are stateful and often the cause of such issues.
- ✗
The VPC route table does not have a route to the on-premises network
Why it's wrong here
EC2 is reachable, so routing is fine.
Visual reference
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Last reviewed: Jul 4, 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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