The correct solution is to use a NAT instance to translate addresses for overlapping CIDR ranges. When a VPC and an on-premises network both use 10.0.0.0/16, a site-to-site VPN would create routing conflicts because the same IP space exists on both sides. A NAT instance resolves this by performing destination NAT (DNAT) on inbound traffic from on-premises, translating it into a non-conflicting IP range inside the VPC, and source NAT (SNAT) on outbound traffic back, effectively hiding the overlap from the routing tables. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of hybrid networking workarounds when renumbering is not an option—a common trap is assuming VPC peering or a simple VPN will suffice, but overlapping CIDR blocks require address translation. Remember the memory tip: “Same CIDR? NAT the traffic.”
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 a VPC with a CIDR block of 10.0.0.0/16. They need to connect to an on-premises network using a site-to-site VPN. The on-premises network uses 10.0.0.0/16 as well. Which solution avoids routing conflicts?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a NAT instance to translate addresses for overlapping ranges.
Option D is correct because a NAT instance can translate the overlapping IP addresses from the on-premises network (10.0.0.0/16) to a different IP range within the VPC, allowing communication without routing conflicts. The NAT instance performs destination NAT (DNAT) for inbound traffic and source NAT (SNAT) for outbound traffic, effectively hiding the overlap. This is a common workaround when both networks use the same CIDR block and cannot be renumbered.
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.
✗
Attach an Internet Gateway and use public IPs for communication.
Why it's wrong here
Internet Gateway doesn't resolve overlap; security concerns.
✗
Set up a second VPN connection to a different virtual private gateway.
Why it's wrong here
Multiple VPNs don't solve IP overlap.
✗
Create a VPC peering connection between the VPC and on-premises network.
Why it's wrong here
Peering requires non-overlapping CIDRs.
✓
Use a NAT instance to translate addresses for overlapping ranges.
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a second VPN connection or VPC peering can solve overlapping CIDR issues, but AWS requires unique, non-overlapping IP ranges for both VPN route propagation and VPC peering, making NAT the only viable option among the choices.
Detailed technical explanation
How to think about this question
Under the hood, a NAT instance uses iptables (or similar) to perform IP masquerading and port forwarding, rewriting source/destination IPs in the IP header. In a site-to-site VPN with overlapping CIDRs, the VPC's route table must have a specific route (e.g., 10.0.0.0/16) pointing to the VPN gateway, but this conflicts with the local VPC route; a NAT instance placed in a separate subnet can translate the on-premises range (e.g., 10.0.0.0/16) to a non-overlapping range (e.g., 172.16.0.0/16) within the VPC. A real-world scenario is when a company acquires another organization with the same private IP space and must interconnect without 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.
Networking and Content Delivery — This question tests Networking and Content Delivery — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a NAT instance to translate addresses for overlapping ranges. — Option D is correct because a NAT instance can translate the overlapping IP addresses from the on-premises network (10.0.0.0/16) to a different IP range within the VPC, allowing communication without routing conflicts. The NAT instance performs destination NAT (DNAT) for inbound traffic and source NAT (SNAT) for outbound traffic, effectively hiding the overlap. This is a common workaround when both networks use the same CIDR block and cannot be renumbered.
What should I do if I get this SOA-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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a VPC with an IPv4 CIDR block of 10.0.0.0/16. They need to connect to an on-premises network with a CIDR of 10.0.0.0/8. What is the issue?
easy
A.The on-premises CIDR is private and cannot be used with AWS.
Why C: Overlapping CIDR blocks prevent VPC peering or VPN connections because routes conflict. Option A is not the issue. Option B is not the primary issue. Option D is not directly a problem.
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This SOA-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 SOA-C02 exam.
Question Discussion
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