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Question 127 of 1,705

Network Design →hardMultiple ChoiceObjective-mapped

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 uses AWS Direct Connect with a private VIF to access a VPC. They also have a site-to-site VPN as backup. They notice that during Direct Connect maintenance, the VPN does not take over traffic as expected. All routes are advertised over BGP. What is the most likely reason?

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.

A
The Direct Connect virtual interface is still in the 'available' state even though the physical link is down.
Why wrong: If the physical link is down, the virtual interface should also be down.
B
The VPN tunnel is using a different BGP ASN than the Direct Connect.
Why wrong: BGP ASN mismatch would prevent the VPN from establishing, but the question states the VPN is a backup and is expected to work.
C
The VPN BGP advertisements have a longer AS PATH than the Direct Connect advertisements, making them less preferred.
BGP prefers the shortest AS PATH, so VPN routes with longer AS PATH are not used when Direct Connect is available. During maintenance, they should become active but may be delayed.
D
The VPN is configured with a higher local preference than Direct Connect.
Why wrong: Typically Direct Connect has a higher local preference to prefer it over VPN.

Full breakdown with real-world context →

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

✓

The VPN BGP advertisements have a longer AS PATH than the Direct Connect advertisements, making them less preferred.

Option C is correct because BGP path selection prefers routes with the shortest AS_PATH. During normal operation, the Direct Connect private VIF advertises routes with a shorter AS_PATH than the VPN backup. When the Direct Connect physical link goes down, the BGP session over the private VIF also goes down, and the VPN routes should take over. However, if the VPN BGP advertisements have a longer AS_PATH, they remain less preferred in the BGP routing table, and the router may still try to use the now-unreachable Direct Connect routes until they are withdrawn, causing traffic to drop instead of failing 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.

✗
The Direct Connect virtual interface is still in the 'available' state even though the physical link is down.
Why it's wrong here
If the physical link is down, the virtual interface should also be down.
✗
The VPN tunnel is using a different BGP ASN than the Direct Connect.
Why it's wrong here
BGP ASN mismatch would prevent the VPN from establishing, but the question states the VPN is a backup and is expected to work.
✓
The VPN BGP advertisements have a longer AS PATH than the Direct Connect advertisements, making them less preferred.
Why this is correct
BGP prefers the shortest AS PATH, so VPN routes with longer AS PATH are not used when Direct Connect is available. During maintenance, they should become active but may be delayed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The VPN is configured with a higher local preference than Direct Connect.
Why it's wrong here
Typically Direct Connect has a higher local preference to prefer it over VPN.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume BGP failover is automatic based on reachability, but BGP path selection is deterministic and based on attribute comparison; without explicit tuning (e.g., local preference or AS_PATH prepending), the backup path with a longer AS_PATH will never be used as long as the primary path's routes are still in the routing table, even if the primary path is down.

Detailed technical explanation

How to think about this question

BGP path selection uses multiple attributes; when AS_PATH lengths are equal, it then compares MED, eBGP vs iBGP, IGP metric to next hop, and so on. In a Direct Connect with VPN backup scenario, the Direct Connect provider often prepends its own ASN to the AS_PATH, but the VPN BGP advertisements may traverse multiple ISP hops, resulting in a longer AS_PATH. A common real-world mitigation is to use BGP communities or local preference on the VPN side to override the AS_PATH length, ensuring failover works correctly.

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 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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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: The VPN BGP advertisements have a longer AS PATH than the Direct Connect advertisements, making them less preferred. — Option C is correct because BGP path selection prefers routes with the shortest AS_PATH. During normal operation, the Direct Connect private VIF advertises routes with a shorter AS_PATH than the VPN backup. When the Direct Connect physical link goes down, the BGP session over the private VIF also goes down, and the VPN routes should take over. However, if the VPN BGP advertisements have a longer AS_PATH, they remain less preferred in the BGP routing table, and the router may still try to use the now-unreachable Direct Connect routes until they are withdrawn, causing traffic to drop instead of failing 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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". 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?

Read the scenario before looking for a memorised answer.

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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.