The answer is to configure AS_PATH prepending on the VPN BGP advertisements from the on-premises router. This works because BGP path selection prefers the shortest AS_PATH length; by artificially lengthening the VPN’s AS_PATH, the Direct Connect route remains the shorter, preferred path for all traffic. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of BGP route manipulation to make Direct Connect preferred over VPN, a common design for hybrid networking. A frequent trap is assuming you can set local preference in AWS, but that attribute is only honored on the customer side, not within AWS. Instead, AS_PATH prepending is the standard, reliable method to deprioritize a backup VPN without disabling it entirely. Memory tip: think of AS_PATH prepending as adding “extra hops” to the VPN route, making BGP naturally choose the more direct Direct Connect path.
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 has an AWS Direct Connect connection with a private VIF to a VPC. The VPC has multiple subnets across two Availability Zones. The company wants to use the Direct Connect connection as the primary path for all traffic from on-premises to the VPC, and use a Site-to-Site VPN as a backup. The on-premises router is configured to advertise a default route via BGP over the Direct Connect, and the VPN also advertises a default route. Which configuration ensures that the Direct Connect path is preferred over the VPN?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure AS_PATH prepending on the VPN BGP advertisements from the on-premises router to make the VPN path longer.
Option C is correct because by default, BGP routes from Direct Connect have a lower MED if not set, but the VPN may also have lower metrics. The most reliable way is to prepend AS_PATH on the VPN BGP advertisements to make them less preferred. Option A is wrong because local preference is typically set on the router, not in AWS. Option B is wrong because decreasing the MED on the Direct Connect side would make it more preferred, but it's not a standard approach; AS_PATH prepending is more straightforward. Option D is wrong because disabling route propagation on the VPN route table would prevent the VPN routes from being used at all, but does not affect the BGP path selection.
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.
✗
Disable route propagation from the VPN in the VPC route tables to ensure Direct Connect routes take precedence.
Why it's wrong here
This would remove VPN routes altogether, not provide failover.
✗
Set a higher local preference on the Direct Connect BGP session on the on-premises router.
Why it's wrong here
Local preference is not directly controlled by AWS configuration.
✗
Decrease the Multi-Exit Discriminator (MED) value on the Direct Connect BGP advertisements from AWS.
Why it's wrong here
MED is not typically set by AWS; it's more common to adjust on-premises.
✓
Configure AS_PATH prepending on the VPN BGP advertisements from the on-premises router to make the VPN path longer.
Why this is correct
Longer AS_PATH makes the route less preferred.
Clue confirmation
The clue word "primary" in the question point toward this answer.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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: Configure AS_PATH prepending on the VPN BGP advertisements from the on-premises router to make the VPN path longer. — Option C is correct because by default, BGP routes from Direct Connect have a lower MED if not set, but the VPN may also have lower metrics. The most reliable way is to prepend AS_PATH on the VPN BGP advertisements to make them less preferred. Option A is wrong because local preference is typically set on the router, not in AWS. Option B is wrong because decreasing the MED on the Direct Connect side would make it more preferred, but it's not a standard approach; AS_PATH prepending is more straightforward. Option D is wrong because disabling route propagation on the VPN route table would prevent the VPN routes from being used at all, but does not affect the BGP path selection.
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: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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 →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a Direct Connect connection with a private virtual interface (VIF) to a VPC. They have also set up a Site-to-Site VPN as a backup. The VPC has a virtual private gateway (VGW) attached. The on-premises network uses BGP over the Direct Connect and static routes for the VPN. The network engineer notices that traffic from the VPC to on-premises is not using the Direct Connect when it is available; instead, it goes over the VPN. The VPC route table has a route for the on-premises CIDR (10.0.0.0/8) to the VGW. The VPN connection is configured with static routes. What is the MOST likely cause of this behavior?
medium
✓ A.The VPN static route has higher precedence than the BGP route from Direct Connect
B.The VPC route table does not have a route for the on-premises CIDR
C.The VGW is not attached to the VPC
D.The Direct Connect virtual interface is not associated with the VGW
Why A: Option D is correct. When using a VGW, AWS automatically propagates routes from the Direct Connect virtual interface and the VPN connection into the VPC route table. If both routes are propagated, the VPN route (static) may have a lower metric or be preferred due to BGP attributes? Actually, by default, AWS prefers the more specific route. But here both are to the same CIDR? The on-premises CIDR is 10.0.0.0/8. The Direct Connect virtual interface advertises this via BGP. The VPN static route also specifies this CIDR. AWS route tables use the longest prefix match, but if both routes have the same prefix length, the one with the lower BGP metric (if BGP) or the static route? Actually, static routes have higher precedence than propagated routes. So the static route from the VPN would be preferred over the BGP route from Direct Connect. That is the issue. The engineer should either remove the static route from the VPN or use BGP on the VPN to allow path selection. Option A is incorrect because both are to the VGW. Option B is incorrect because the VGW is attached. Option C is incorrect because the VPC route table does have a route.
Last reviewed: Jun 20, 2026
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