This ANS-C01 practice question tests your understanding of network implementation. 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 network engineer is setting up a Direct Connect connection from an on-premises data center to AWS. The connection uses a private VIF to connect to a VPC via a Direct Connect gateway. The on-premises network is advertising a BGP prefix 10.0.0.0/16, which overlaps with the VPC CIDR 10.0.0.0/16. What is the expected behavior?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The BGP session will be established, but the overlapping prefix will be ignored and not programmed into the VPC route tables.
Option A is correct because AWS Direct Connect with a private VIF will not accept BGP prefixes that overlap with the VPC CIDR. Option B, C, and D are incorrect as they describe behaviors that do not occur in this scenario.
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 VPC will automatically reassign a new CIDR to avoid the conflict.
Why it's wrong here
AWS does not automatically modify VPC CIDRs.
✗
The BGP session will fail to establish due to the prefix conflict.
Why it's wrong here
BGP session establishment is not affected by prefix overlap; only route advertisement is rejected.
✓
The BGP session will be established, but the overlapping prefix will be ignored and not programmed into the VPC route tables.
Why this is correct
AWS does not allow overlapping prefixes to be injected into VPC route tables to prevent routing conflicts.
The on-premises prefix will take precedence and override the VPC route.
Why it's wrong here
AWS prioritizes local VPC routes over learned routes, so the VPC CIDR remains.
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 BGP session will be established, but the overlapping prefix will be ignored and not programmed into the VPC route tables. — Option A is correct because AWS Direct Connect with a private VIF will not accept BGP prefixes that overlap with the VPC CIDR. Option B, C, and D are incorrect as they describe behaviors that do not occur in this scenario.
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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Question Discussion
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