- A
The secondary VIF is not configured with BGP authentication.
Why wrong: BGP authentication does not affect path selection.
- B
AS_PATH prepending on the AWS side only affects outbound traffic, not inbound traffic.
AS_PATH prepending on AWS side makes the path longer for outbound traffic from AWS to on-premises. To affect inbound traffic, prepending must be done on the on-premises router.
- C
The BGP hold time timer is set too low, causing the primary connection to flap.
Why wrong: Hold time timers do not affect path selection if the connection is stable.
- D
The company did not set the MED attribute on the primary VIF.
Why wrong: MED is used to influence inbound traffic, but it is not set by default and would need to be configured on the on-premises side.
- E
The company configured the prepending on the virtual private gateway instead of the Direct Connect gateway.
Why wrong: Prepending is configured on the VIF association with the virtual private gateway, not on the gateway itself. Location does not change the effect.
ANS-C01 AS_PATH Prepending 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. A key principle to apply: aS_PATH Prepending. 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 connected to a VPC. The company wants to add a second Direct Connect connection for redundancy. They plan to use BGP AS_PATH prepending to influence traffic steering so that the primary connection is preferred for inbound traffic. The on-premises router advertises the same prefix over both connections. The company configures BGP on the primary VIF with AS_PATH prepending (prepend two AS numbers). However, after configuration, inbound traffic still uses both paths equally. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
AS_PATH prepending on the AWS side only affects outbound traffic, not inbound traffic.
Option B is correct. AS_PATH prepending on the AWS side (the VIF) affects the AS_PATH attribute of routes that AWS advertises to the on-premises router. However, these routes are used by the on-premises router for outbound traffic from the on-premises network to AWS, not for inbound traffic from AWS to on-prem. Inbound traffic (from AWS to on-prem) is controlled by the BGP routes that AWS receives from the on-premises router, which are not affected by the prepending on the AWS side. Therefore, the prepending does not influence inbound traffic steering, and both paths are still used equally for inbound traffic.
Key principle: AS_PATH Prepending
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 secondary VIF is not configured with BGP authentication.
Why it's wrong here
BGP authentication does not affect path selection.
- ✓
AS_PATH prepending on the AWS side only affects outbound traffic, not inbound traffic.
Why this is correct
AS_PATH prepending on AWS side makes the path longer for outbound traffic from AWS to on-premises. To affect inbound traffic, prepending must be done on the on-premises router.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
AS_PATH Prepending
- ✗
The BGP hold time timer is set too low, causing the primary connection to flap.
Why it's wrong here
Hold time timers do not affect path selection if the connection is stable.
- ✗
The company did not set the MED attribute on the primary VIF.
Why it's wrong here
MED is used to influence inbound traffic, but it is not set by default and would need to be configured on the on-premises side.
- ✗
The company configured the prepending on the virtual private gateway instead of the Direct Connect gateway.
Why it's wrong here
Prepending is configured on the VIF association with the virtual private gateway, not on the gateway itself. Location does not change the effect.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common trap is to assume that AS_PATH prepending on the AWS side directly controls inbound traffic from on-premises. In reality, it only influences the BGP advertisements for outbound traffic from on-premises to AWS. Inbound traffic (AWS to on-prem) is determined by the routes AWS receives, so prepending on the AWS side has no effect on inbound traffic.
Detailed technical explanation
How to think about this question
In BGP, AS_PATH prepending artificially lengthens the AS_PATH attribute, making a route less preferred by BGP's path selection algorithm (shorter AS_PATH is preferred). However, this only affects the direction in which the prepended route is advertised. When you prepend on the AWS side, you are modifying the AS_PATH of routes that AWS sends to the on-premises router. The on-premises router then sees a longer path for the primary VIF and should prefer the secondary VIF for traffic destined to the VPC. If the on-premises router still uses both paths, it may be because the on-premises router has a higher local preference for the primary path, or because the on-premises router is not using BGP best path selection as expected (e.g., it might be using a different tie-breaker like IGP metric). In a real-world scenario, you might need to combine prepending with other attributes like MED or local preference on the on-premises side to achieve deterministic inbound traffic steering.
KKey Concepts to Remember
- AS_PATH Prepending
- Inbound Traffic Steering
- Direct Connect Virtual Interface (VIF)
- BGP Best Path Selection
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
AS_PATH Prepending
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review aS_PATH Prepending, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — AS_PATH Prepending.
What is the correct answer to this question?
The correct answer is: AS_PATH prepending on the AWS side only affects outbound traffic, not inbound traffic. — Option B is correct. AS_PATH prepending on the AWS side (the VIF) affects the AS_PATH attribute of routes that AWS advertises to the on-premises router. However, these routes are used by the on-premises router for outbound traffic from the on-premises network to AWS, not for inbound traffic from AWS to on-prem. Inbound traffic (from AWS to on-prem) is controlled by the BGP routes that AWS receives from the on-premises router, which are not affected by the prepending on the AWS side. Therefore, the prepending does not influence inbound traffic steering, and both paths are still used equally for inbound traffic.
What should I do if I get this ANS-C01 question wrong?
Review aS_PATH Prepending, then practise related ANS-C01 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "primary". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
AS_PATH Prepending
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Last reviewed: Jun 30, 2026
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