This ANS-C01 practice question tests your understanding of network design. 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 uses AWS Direct Connect to connect its on-premises network to a VPC. They have a private VIF attached to a virtual private gateway. They want to use AWS Site-to-Site VPN as a backup connection. Which configuration ensures automatic failover?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use BGP on both the Direct Connect private VIF and the VPN connection, and advertise the same prefixes with a longer AS path for the VPN.
Option C is correct because using BGP on both the Direct Connect private VIF and the VPN connection allows you to manipulate route selection via AS path prepending. By advertising the same prefixes with a longer AS path on the VPN, the Direct Connect path is preferred, and if it fails, BGP withdraws the routes, causing traffic to automatically fail over to the VPN.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Attach the VPN connection to a separate virtual private gateway and use a transit gateway to combine them.
Why it's wrong here
This complicates failover; using same VGW is simpler.
✗
Use static routes on the Direct Connect private VIF and BGP on the VPN connection.
Why it's wrong here
Static routes do not fail over automatically.
✓
Use BGP on both the Direct Connect private VIF and the VPN connection, and advertise the same prefixes with a longer AS path for the VPN.
Read the scenario before looking for a memorised answer.
✗
Create a second Direct Connect connection and use equal-cost multipath (ECMP) between the two.
Why it's wrong here
This does not provide a backup; both are primary.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that static routes can provide automatic failover, but static routes lack dynamic withdrawal, so BGP must be used on both connections with AS path prepending to ensure automatic and predictable failover.
Detailed technical explanation
How to think about this question
Under the hood, BGP on the private VIF and VPN connection uses the same virtual private gateway (VGW), which allows the VGW to learn routes from both connections. By prepending the AS path on the VPN routes (e.g., adding multiple AS numbers), the BGP best path selection algorithm (RFC 4271) deprioritizes the VPN path, ensuring Direct Connect is preferred. In a real-world scenario, if the Direct Connect link goes down, BGP sessions on the private VIF are lost, the routes are withdrawn, and the VGW immediately uses the VPN routes, achieving sub-second failover.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use BGP on both the Direct Connect private VIF and the VPN connection, and advertise the same prefixes with a longer AS path for the VPN. — Option C is correct because using BGP on both the Direct Connect private VIF and the VPN connection allows you to manipulate route selection via AS path prepending. By advertising the same prefixes with a longer AS path on the VPN, the Direct Connect path is preferred, and if it fails, BGP withdraws the routes, causing traffic to automatically fail over to the VPN.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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