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Question 127 of 1,705

Network Design →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is that the VPN BGP advertisements have a longer AS PATH than the Direct Connect advertisements, making them less preferred. BGP selects the best route based on the shortest AS PATH length when all other attributes are equal, so if the VPN path traverses more autonomous systems, it will be deprioritized even when Direct Connect fails, unless the VPN’s local preference is explicitly raised. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of BGP route selection between Direct Connect and VPN failover scenarios, where candidates often mistakenly assume the VPN will automatically take over during maintenance. A common trap is forgetting that BGP’s AS PATH attribute is checked before local preference in the decision process, so a longer path on the VPN keeps it inactive. Memory tip: “Path length first, preference second — if the VPN path is long, the backup stays wrong.”

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.

Question 1hardmultiple choice

Open the full BGP breakdown →

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 A is correct because if the Direct Connect and VPN BGP advertisements have the same AS PATH length, the route with the lower local preference is preferred. If local preference is the same, the route with the lower MED is preferred. Typically, Direct Connect routes have a higher local preference by default, so when Direct Connect goes down, the VPN routes are available but may have a lower local preference, causing them to be ignored if the Direct Connect routes are still present. However, the scenario says Direct Connect is down, so the VPN routes should be active. Another common issue is that the VPN BGP session does not come up due to misconfiguration, but the most likely reason is that the VPN's BGP advertisements have a longer AS PATH, making them less preferred. Option B is wrong because the VPN is a backup. Option C is wrong because Direct Connect is down. Option D is wrong because the VPN is expected to have a longer AS PATH.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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
Static NAT maps one inside address to one outside address.
✗
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: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related ANS-C01 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Design — This question tests Network Design — Static NAT maps one inside address to one outside address..

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 A is correct because if the Direct Connect and VPN BGP advertisements have the same AS PATH length, the route with the lower local preference is preferred. If local preference is the same, the route with the lower MED is preferred. Typically, Direct Connect routes have a higher local preference by default, so when Direct Connect goes down, the VPN routes are available but may have a lower local preference, causing them to be ignored if the Direct Connect routes are still present. However, the scenario says Direct Connect is down, so the VPN routes should be active. Another common issue is that the VPN BGP session does not come up due to misconfiguration, but the most likely reason is that the VPN's BGP advertisements have a longer AS PATH, making them less preferred. Option B is wrong because the VPN is a backup. Option C is wrong because Direct Connect is down. Option D is wrong because the VPN is expected to have a longer AS PATH.

What should I do if I get this ANS-C01 question wrong?

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?

Static NAT maps one inside address to one outside address.

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