ANS-C01 Network Security, Compliance and Governance Practice Question
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. 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 have peered this VPC with another VPC using a VPC Peering connection. The peered VPC has a CIDR of 10.0.0.0/16 (overlapping). The company wants to allow communication between specific instances in both VPCs without changing the CIDRs. What should they do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use AWS PrivateLink to create a VPC endpoint service in one VPC and access it from the other VPC
Option D is correct because with overlapping CIDRs, VPC Peering cannot route traffic correctly due to identical CIDR blocks. A Transit Gateway with Network Manager can be used with a VPN connection or Direct Connect to connect the VPCs, but the question asks for a solution to allow communication without changing CIDRs. However, the only way to allow communication with overlapping CIDRs is to use PrivateLink (VPC endpoint services) where one VPC hosts the service and the other VPC accesses it via an endpoint, avoiding routing conflicts. Option A is wrong because security groups do not solve routing issues. Option B is wrong because NAT gateways do not resolve overlapping CIDR routing. Option C is wrong because a Transit Gateway does not resolve overlapping CIDRs without additional configuration like NAT.
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.
✗
Configure a NAT gateway in each VPC
Why it's wrong here
NAT gateways are for outbound internet, not inter-VPC routing with overlapping CIDRs.
✓
Use AWS PrivateLink to create a VPC endpoint service in one VPC and access it from the other VPC
Why this is correct
PrivateLink allows connectivity without IP routing, avoiding CIDR overlap issues.
Use security group references to allow traffic between the instances
Why it's wrong here
Security groups control traffic but do not resolve routing conflicts.
✗
Create a Transit Gateway and attach both VPCs
Why it's wrong here
Transit Gateway cannot route between overlapping CIDRs without additional measures.
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 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.
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 Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use AWS PrivateLink to create a VPC endpoint service in one VPC and access it from the other VPC — Option D is correct because with overlapping CIDRs, VPC Peering cannot route traffic correctly due to identical CIDR blocks. A Transit Gateway with Network Manager can be used with a VPN connection or Direct Connect to connect the VPCs, but the question asks for a solution to allow communication without changing CIDRs. However, the only way to allow communication with overlapping CIDRs is to use PrivateLink (VPC endpoint services) where one VPC hosts the service and the other VPC accesses it via an endpoint, avoiding routing conflicts. Option A is wrong because security groups do not solve routing issues. Option B is wrong because NAT gateways do not resolve overlapping CIDR routing. Option C is wrong because a Transit Gateway does not resolve overlapping CIDRs without additional configuration like NAT.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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