SAP-C02 VPC Peering Practice Question
A large enterprise with multiple business units (BUs) uses AWS Organizations with a shared services account and BU-specific accounts. Each BU account has a VPC with multiple subnets. The shared services account hosts a central NAT gateway that provides outbound internet access to all BU private subnets via VPC peering. Recently, the network team noticed that traffic from one BU's private subnet is being blocked by the security group in the shared services account. They verified that the route tables are correctly configured. What is the most likely cause and solution?
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 VPC peering connection is not in the 'active' state. Recreate the VPC peering connection.
VPC peering connections must be in the 'active' state to route traffic between VPCs. If the peering connection for a specific BU's VPC is not active (e.g., pending acceptance, expired, or deleted), traffic from that BU's private subnet to the shared services VPC will be blocked. Since route tables and the NAT gateway's configuration are correct, the most likely cause is an inactive VPC peering connection. Option B is incorrect because NAT gateways do not support user-modifiable security groups; AWS manages the security group on the NAT gateway's ENI and it cannot be updated by customers. Option A contradicts the verified route tables. Option D would affect all BUs, not just one.
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 BU account's route table does not have a route to the NAT gateway's private IP. Add a route via the VPC peering connection.
Why it's wrong here
This is incorrect because the route tables have been verified as correctly configured. A missing route would affect traffic but has been ruled out.
- ✗
The security group attached to the NAT gateway's ENI does not allow incoming traffic from the BU private subnet. Update the security group to allow inbound traffic from the BU subnet CIDR.
Why it's wrong here
This is incorrect because NAT gateways do not allow user modification of security groups. The security group on the NAT gateway's ENI is managed by AWS and cannot be updated. The issue must involve another layer, such as VPC peering state.
- ✓
The VPC peering connection is not in the 'active' state. Recreate the VPC peering connection.
Why this is correct
This is correct. If the VPC peering connection is not active (e.g., pending acceptance, expired, or deleted), traffic from the BU's VPC to the shared services VPC will be blocked, affecting only that BU's outbound internet access via the central NAT gateway.
- ✗
The NAT gateway's Elastic IP is not attached. Attach an Elastic IP to the NAT gateway.
Why it's wrong here
This is incorrect because the NAT gateway already requires an Elastic IP to function. If the EIP were missing, the NAT gateway would not work at all, affecting all BUs, not just one.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAP-C02 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 SAP-C02 exam.