- A
Check that the security group attached to the RDS instance allows inbound traffic from the CIDR block of VPC A.
Correct: Security groups must allow traffic from peer VPC.
- B
Verify that the network ACLs in both VPCs have appropriate inbound and outbound rules for the traffic.
Why wrong: Wrong: NACLs are already verified correct.
- C
Confirm that the VPCs have an Internet Gateway attached.
Why wrong: Wrong: Internet Gateway is not required for VPC peering.
- D
Check that the EC2 instance has an IAM role that allows it to communicate with RDS.
Why wrong: Wrong: IAM roles are not needed for network connectivity.
- E
Ensure that the VPC peering connection is in the 'active' state.
Correct: Peering must be active for traffic to flow.
Question 467 of 1,705
VPC Peering Connectivity Troubleshooting: Check Peering State and Security Group Inbound Rules
This ANS-C01 practice question tests your understanding of network security, compliance and governance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: vPC Peering. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer is troubleshooting connectivity between two VPCs connected via a VPC peering connection. Security groups and NACLs are configured correctly. The engineer verifies that the route tables have the necessary entries. However, traffic from an EC2 instance in VPC A to an RDS instance in VPC B fails. Which TWO additional checks should be performed? (Choose two.)
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
✓
Check that the security group attached to the RDS instance allows inbound traffic from the CIDR block of VPC A.
The correct checks to perform when troubleshooting VPC peering connectivity are to ensure the VPC peering connection is in the 'active' state (Option E) and that the security group attached to the RDS instance allows inbound traffic from the CIDR block of VPC A (Option A). Without an active peer connection, traffic cannot flow even if route tables are correct. Similarly, security group rules are stateful and must explicitly permit inbound traffic; NACLs are stateless but since the issue is within the same VPC peering, security groups are a likely culprit. IAM roles and Internet Gateways are not required for VPC peering traffic.
Key principle: VPC Peering
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check that the security group attached to the RDS instance allows inbound traffic from the CIDR block of VPC A.
Why this is correct
Correct: Security groups must allow traffic from peer VPC.
Related concept
VPC Peering
- ✗
Verify that the network ACLs in both VPCs have appropriate inbound and outbound rules for the traffic.
Why it's wrong here
Wrong: NACLs are already verified correct.
- ✗
Confirm that the VPCs have an Internet Gateway attached.
Why it's wrong here
Wrong: Internet Gateway is not required for VPC peering.
- ✗
Check that the EC2 instance has an IAM role that allows it to communicate with RDS.
Why it's wrong here
Wrong: IAM roles are not needed for network connectivity.
- ✓
Ensure that the VPC peering connection is in the 'active' state.
Why this is correct
Correct: Peering must be active for traffic to flow.
Related concept
VPC Peering
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- VPC Peering
- Security Group Inbound Rules
- VPC Peering Connection States
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
VPC Peering
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review vPC Peering, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — VPC Peering.
What is the correct answer to this question?
The correct answer is: Check that the security group attached to the RDS instance allows inbound traffic from the CIDR block of VPC A. — The correct checks to perform when troubleshooting VPC peering connectivity are to ensure the VPC peering connection is in the 'active' state (Option E) and that the security group attached to the RDS instance allows inbound traffic from the CIDR block of VPC A (Option A). Without an active peer connection, traffic cannot flow even if route tables are correct. Similarly, security group rules are stateful and must explicitly permit inbound traffic; NACLs are stateless but since the issue is within the same VPC peering, security groups are a likely culprit. IAM roles and Internet Gateways are not required for VPC peering traffic.
What should I do if I get this ANS-C01 question wrong?
Review vPC Peering, then practise related ANS-C01 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
VPC Peering
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Last reviewed: Jun 20, 2026
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