- A
Use AS_PATH prepending on the on-premises BGP advertisements to make them less preferred
Why wrong: Incorrect; AS_PATH prepending affects BGP path selection but longest prefix match overrides it.
- B
No additional configuration is needed; the more specific route will be preferred automatically
Correct; Transit Gateway uses longest prefix match, so the /16 from VPC is preferred over /8 from on-premises.
- C
Add a static route in the Transit Gateway route table for 10.0.0.0/16 pointing to the VPC attachment
Why wrong: Incorrect; the more specific route from the VPC attachment is already preferred.
- D
Disable route propagation from the Direct Connect virtual interface to the Transit Gateway
Why wrong: Incorrect; disabling propagation would remove the on-premises routes completely, which may not be desired.
Quick Answer
The answer is that no additional configuration is needed, as the more specific route will be preferred automatically. This is correct because AWS Transit Gateway uses longest prefix match routing, so the VPC’s 10.0.0.0/16 is more specific than the on-premises 10.0.0.0/8, and traffic destined for that range will always go to the VPC without manual intervention. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how overlapping CIDR between VPC and on-premises via Transit Gateway is resolved by fundamental IP routing logic, not by BGP attributes like AS_PATH prepending. A common trap is assuming you need to manipulate BGP or add static routes, but the exam expects you to recognize that longest prefix match automatically handles the conflict. Memory tip: think "more bits win" — a /16 always beats a /8 for the same starting address.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 is building a hybrid network with an AWS Transit Gateway connecting multiple VPCs and an on-premises network via Direct Connect. The on-premises network uses BGP to advertise routes to the Transit Gateway. One of the VPCs has an overlapping CIDR (10.0.0.0/16) with the on-premises network (10.0.0.0/8). The company wants to ensure that traffic from other VPCs to 10.0.0.0/16 goes to the VPC, not on-premises. What configuration is required?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
No additional configuration is needed; the more specific route will be preferred automatically
Option C is correct because Transit Gateway uses longest prefix match. The VPC's /16 is more specific than the on-premises /8, so traffic to 10.0.0.0/16 will automatically go to the VPC. No additional configuration is needed. Option A is wrong because disabling route propagation would remove the on-premises routes entirely. Option B is wrong because a static route is not needed; longest prefix match already handles it. Option D is wrong because AS_PATH prepending is used to influence BGP path selection, but in this case, longest prefix match is sufficient.
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.
- ✗
Use AS_PATH prepending on the on-premises BGP advertisements to make them less preferred
Why it's wrong here
Incorrect; AS_PATH prepending affects BGP path selection but longest prefix match overrides it.
- ✓
No additional configuration is needed; the more specific route will be preferred automatically
- ✗
Add a static route in the Transit Gateway route table for 10.0.0.0/16 pointing to the VPC attachment
Why it's wrong here
Incorrect; the more specific route from the VPC attachment is already preferred.
- ✗
Disable route propagation from the Direct Connect virtual interface to the Transit Gateway
Why it's wrong here
Incorrect; disabling propagation would remove the on-premises routes completely, which may not be desired.
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: No additional configuration is needed; the more specific route will be preferred automatically — Option C is correct because Transit Gateway uses longest prefix match. The VPC's /16 is more specific than the on-premises /8, so traffic to 10.0.0.0/16 will automatically go to the VPC. No additional configuration is needed. Option A is wrong because disabling route propagation would remove the on-premises routes entirely. Option B is wrong because a static route is not needed; longest prefix match already handles it. Option D is wrong because AS_PATH prepending is used to influence BGP path selection, but in this case, longest prefix match is sufficient.
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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Last reviewed: Jun 20, 2026
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.
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