The answer is to verify that the prefix is included in the allowed prefixes list for the Direct Connect virtual interface. When a BGP session is established but a specific /24 prefix from on-premises is not propagated into the VPC route tables, the most common cause is that the virtual private gateway (VGW) is configured with an allowed prefixes list that explicitly filters out any routes not on that list. This list acts as a whitelist, and even though the BGP session is up and the ASN is correct, the VGW will silently reject any prefix not matching the list, preventing it from appearing in the VPC route tables. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of the Direct Connect route advertisement mechanism, which differs from VPN route propagation. A common trap is to assume the BGP session being established means all routes are accepted, but the allowed prefixes list is a separate, mandatory filter. Memory tip: think of the allowed prefixes list as a bouncer at the VGW door—the BGP session gets you in the building, but the list decides which prefixes get on the dance floor.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 has a Direct Connect connection with a private VIF to a VPC. They want to use BGP to advertise a specific /24 prefix from their on-premises network to AWS. After configuration, the prefix is not visible in the VPC route tables. The BGP session is established. What should the company check?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Verify that the prefix is included in the allowed prefixes list for the Direct Connect virtual interface
Option A is correct because the prefix must be allowed by the allowed prefixes list on the virtual private gateway; otherwise, it will not be propagated. Option B is wrong because the BGP session is established, so ASN is not an issue. Option C is wrong because route propagation is for VPN, not Direct Connect. Option D is wrong because the VPC route table can have custom routes, but the virtual private gateway will not accept prefixes not in the allowed list.
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.
✓
Verify that the prefix is included in the allowed prefixes list for the Direct Connect virtual interface
Why this is correct
The virtual private gateway only accepts prefixes that are in the allowed prefix list.
Related concept
Read the scenario before looking for a memorised answer.
✗
Ensure that route propagation is enabled on the VPC route table
Why it's wrong here
Route propagation is for VPN connections, not Direct Connect private VIF.
✗
Check that the BGP ASN on the customer gateway is unique and not conflicting
Add a static route in the VPC route table for the on-premises prefix
Why it's wrong here
Static routes are not used with Direct Connect; the virtual private gateway automatically propagates routes that are in the allowed list.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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.
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Verify that the prefix is included in the allowed prefixes list for the Direct Connect virtual interface — Option A is correct because the prefix must be allowed by the allowed prefixes list on the virtual private gateway; otherwise, it will not be propagated. Option B is wrong because the BGP session is established, so ASN is not an issue. Option C is wrong because route propagation is for VPN, not Direct Connect. Option D is wrong because the VPC route table can have custom routes, but the virtual private gateway will not accept prefixes not in the allowed list.
What should I do if I get this ANS-C01 question wrong?
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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