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 company has a Direct Connect connection with a private VIF to a VPC. The on-premises network uses BGP to advertise its prefixes. Recently, the on-premises router started advertising a more specific route (10.0.0.0/24) that overlaps with the VPC's CIDR (10.0.0.0/16). What is the impact on traffic destined to 10.0.0.5?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Return traffic from the instance to on-premises is routed through Direct Connect instead of staying within the VPC.
Option C is correct because when a Direct Connect virtual interface advertises a more specific route that overlaps with the VPC CIDR, AWS prefers the more specific route from Direct Connect, causing traffic from the VPC to the on-premises network to be routed via Direct Connect instead of locally. Option A is wrong because the instance remains reachable from on-premises. Option B is wrong because BGP does not cause route flapping in this scenario. Option D is wrong because the traffic is not blackholed; it goes to on-premises.
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 instance becomes unreachable from on-premises.
Why it's wrong here
On-premises still has connectivity.
✓
Return traffic from the instance to on-premises is routed through Direct Connect instead of staying within the VPC.
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: Return traffic from the instance to on-premises is routed through Direct Connect instead of staying within the VPC. — Option C is correct because when a Direct Connect virtual interface advertises a more specific route that overlaps with the VPC CIDR, AWS prefers the more specific route from Direct Connect, causing traffic from the VPC to the on-premises network to be routed via Direct Connect instead of locally. Option A is wrong because the instance remains reachable from on-premises. Option B is wrong because BGP does not cause route flapping in this scenario. Option D is wrong because the traffic is not blackholed; it goes to on-premises.
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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