- A
Use BGP on Direct Connect and static routes on the VPN connection, with a higher metric for the VPN static route.
Why wrong: Static routes for the VPN would not dynamically fail back or handle failure detection as reliably as BGP.
- B
Configure static routes on the customer gateway device with a lower metric for the Direct Connect interface.
Why wrong: Static routes require manual intervention or external automation to detect failure and update routing tables, making failover less reliable.
- C
Use BGP on both connections and prepend AS paths on the Direct Connect routes to make them less preferred.
AS path prepending makes Direct Connect routes less preferred, so VPN routes are used when Direct Connect is up. When Direct Connect fails, BGP sessions drop, and VPN routes become available automatically.
- D
Use BGP on both connections and set a lower local preference on the Direct Connect routes.
Why wrong: Local preference is a BGP attribute that can influence route selection, but VPN connections typically do not support BGP; also, adjusting local preference is less standard than AS path prepending.
ANS-C01 Network Design Practice Question
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 is designing a hybrid network with AWS Direct Connect and AWS Site-to-Site VPN as backup. The primary Direct Connect connection uses a private VIF to a VPC. If the Direct Connect fails, traffic should automatically fail over to the VPN connection. What is the MOST reliable way to achieve this failover?
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 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
Use BGP on both connections and prepend AS paths on the Direct Connect routes to make them less preferred.
Option C is correct because using BGP on both connections allows you to influence route selection via AS path prepending. By prepending the AS path on the Direct Connect routes, you make them appear less preferred compared to the VPN routes, ensuring that under normal conditions traffic uses Direct Connect. When Direct Connect fails, the BGP session drops, the routes are withdrawn, and traffic automatically fails over to the VPN without any manual intervention or reliance on static metrics.
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.
- ✗
Use BGP on Direct Connect and static routes on the VPN connection, with a higher metric for the VPN static route.
- ✗
Configure static routes on the customer gateway device with a lower metric for the Direct Connect interface.
Why it's wrong here
Static routes require manual intervention or external automation to detect failure and update routing tables, making failover less reliable.
- ✓
Use BGP on both connections and prepend AS paths on the Direct Connect routes to make them less preferred.
Why this is correct
AS path prepending makes Direct Connect routes less preferred, so VPN routes are used when Direct Connect is up. When Direct Connect fails, BGP sessions drop, and VPN routes become available automatically.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use BGP on both connections and set a lower local preference on the Direct Connect routes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse local preference (which influences inbound traffic from BGP peers) with AS path prepending (which influences outbound route selection from the perspective of the BGP router), or they assume static metrics provide reliable failover without considering that static routes do not dynamically withdraw on link failure.
Detailed technical explanation
How to think about this question
BGP AS path prepending works by adding repeated AS numbers to the AS_PATH attribute, increasing the path length and making the route less preferred according to the BGP best path selection algorithm (shorter AS_PATH is preferred). In a hybrid Direct Connect and VPN setup, the customer gateway device (CGW) typically runs BGP with both the Direct Connect virtual interface (VIF) and the VPN tunnel endpoint; by prepending on the Direct Connect side (e.g., adding three copies of the customer ASN), the Direct Connect routes become less attractive than the VPN routes, which have a shorter AS_PATH. This technique is widely used in multi-homed BGP designs to control outbound traffic flow without relying on static metrics that cannot adapt to link failures.
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 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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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 connections and prepend AS paths on the Direct Connect routes to make them less preferred. — Option C is correct because using BGP on both connections allows you to influence route selection via AS path prepending. By prepending the AS path on the Direct Connect routes, you make them appear less preferred compared to the VPN routes, ensuring that under normal conditions traffic uses Direct Connect. When Direct Connect fails, the BGP session drops, the routes are withdrawn, and traffic automatically fails over to the VPN without any manual intervention or reliance on static metrics.
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.
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?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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