The answer is to set up a NAT gateway in each VPC and route traffic through the transit gateway using private IP addresses from a separate CIDR block. This solution works because each NAT gateway performs source network address translation (SNAT), converting the overlapping private IPs into unique private IPs from a distinct, non-overlapping CIDR range before traffic enters the transit gateway. By doing so, the transit gateway can forward packets without routing conflicts, as the translated source addresses are globally unique across all attachments. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to handle overlapping CIDR VPC connectivity without re-architecting existing networks—a common challenge in multi-account environments. A frequent trap is assuming you can simply use VPC peering or direct transit gateway attachments, but those fail with overlapping ranges. Memory tip: think “SNAT to un-NAT” — translate overlapping IPs before they reach the gateway to avoid a routing spat.
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 company has multiple AWS accounts that each have their own VPCs with overlapping CIDR ranges. They want to use AWS Transit Gateway to connect these VPCs to a central network account. However, overlapping CIDRs prevent attachment. What is the MOST scalable solution?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set up a NAT gateway in each VPC and route traffic through the transit gateway using private IP addresses from a separate CIDR block.
Option C is correct because it uses a NATgateway in each VPC to translate overlapping private IPs to unique private IPs from a separate CIDR block before routing through the Transit Gateway. This allows the Transit Gateway to forward traffic without conflict, as the NAT gateway performs source network address translation (SNAT) to eliminate IP overlap. This approach is highly scalable because it avoids re-architecting existing VPCs and can be applied incrementally as new VPCs are added.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use AWS PrivateLink to connect each VPC to the network account.
Why it's wrong here
PrivateLink does not solve general IP overlap for all traffic.
✗
Create VPC peering connections between each VPC and the network account.
Why it's wrong here
Peering also requires non-overlapping CIDRs for communication.
✓
Set up a NAT gateway in each VPC and route traffic through the transit gateway using private IP addresses from a separate CIDR block.
Why this is correct
NAT translates overlapping IPs to unique addresses, enabling communication.
Related concept
Read the scenario before looking for a memorised answer.
✗
Assign new non-overlapping CIDR ranges to each VPC and update all resources.
Why it's wrong here
Re-IPing is disruptive and not scalable for many accounts.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume Transit Gateway can handle overlapping CIDRs natively, but it cannot; the NAT gateway is required to perform address translation before traffic enters the Transit Gateway, and this is the most scalable solution without renumbering VPCs.
Detailed technical explanation
How to think about this question
The NATgateway performs SNAT (Source Network Address Translation) to map overlapping source IPs to unique IPs from a separate CIDR block (e.g., 100.64.0.0/10 or a custom range), which are then routed through the Transit Gateway. The Transit Gateway itself does not perform NAT; it relies on the NAT gateway to resolve IP conflicts before traffic enters the TGW. This design is commonly used in multi-account architectures where VPCs have overlapping RFC 1918 addresses, and it avoids the need for complex routing policies or VPC renumbering.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set up a NAT gateway in each VPC and route traffic through the transit gateway using private IP addresses from a separate CIDR block. — Option C is correct because it uses a NAT gateway in each VPC to translate overlapping private IPs to unique private IPs from a separate CIDR block before routing through the Transit Gateway. This allows the Transit Gateway to forward traffic without conflict, as the NAT gateway performs source network address translation (SNAT) to eliminate IP overlap. This approach is highly scalable because it avoids re-architecting existing VPCs and can be applied incrementally as new VPCs are added.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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