The correct answer is that the branch subnets 10.0.1.0/24 and 10.0.2.0/24 overlap with the VPC CIDR of 10.0.0.0/16, causing a routing conflict where the VPC routes traffic locally instead of through the Client VPN. When troubleshooting Client VPN with overlapping CIDRs, the core issue is that the VPC’s main route table contains a local route for the entire 10.0.0.0/16 block, which takes precedence over any VPN route. Because Branch A’s subnet (10.0.1.0/24) and Branch B’s subnet (10.0.2.0/24) fall within that local range, traffic between the branches is directed internally within the VPC rather than being forwarded to the Client VPN endpoint for inter-branch communication. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of route priority and CIDR overlap—a common trap is assuming that adding specific VPN routes will override the implicit local route. A reliable memory tip: “Local wins over VPN when CIDRs are kin”—if a branch subnet is a subset of the VPC CIDR, the VPC will always treat it as local, breaking cross-branch connectivity.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 an IPv4 CIDR block of 10.0.0.0/16. They need to connect two separate branch offices using AWS Client VPN. Each branch office has a different subnet: Branch A uses 10.0.1.0/24 and Branch B uses 10.0.2.0/24. The Client VPN endpoint is configured with a CIDR range of 10.0.3.0/24. The route table for the VPC has the local route and routes to the Client VPN endpoint. Users from both branches can connect to the VPN but cannot communicate with each other. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The branch subnets 10.0.1.0/24 and 10.0.2.0/24 are part of the VPC CIDR, so the VPC routes traffic locally instead of via the VPN
Branch subnets overlap with the VPC CIDR, causing routing conflicts. The VPC sees 10.0.1.0/24 and 10.0.2.0/24 as local, thus traffic destined to those addresses is routed locally within the VPC, not to the VPN. Options B and C are not relevant to inter-branch communication. Option D would not cause the issue because branch subnets are within the VPC CIDR.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 branch subnets 10.0.1.0/24 and 10.0.2.0/24 are part of the VPC CIDR, so the VPC routes traffic locally instead of via the VPN
Why this is correct
Local routes take precedence.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The security group for the Client VPN endpoint does not allow inbound traffic from branch subnets
Why it's wrong here
Security group would affect all traffic, not just inter-branch.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The branch subnets 10.0.1.0/24 and 10.0.2.0/24 are part of the VPC CIDR, so the VPC routes traffic locally instead of via the VPN — Branch subnets overlap with the VPC CIDR, causing routing conflicts. The VPC sees 10.0.1.0/24 and 10.0.2.0/24 as local, thus traffic destined to those addresses is routed locally within the VPC, not to the VPN. Options B and C are not relevant to inter-branch communication. Option D would not cause the issue because branch subnets are within the VPC CIDR.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.