- A
Associate VPC A's and VPC B's route tables with a different Transit Gateway route table that has a default route pointing to the VPC C attachment.
Why wrong: This would affect all traffic, not just between A and B.
- B
Add a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole.
This prevents VPC A from directly reaching VPC B via the Transit Gateway.
- C
Enable route propagation for VPC A and VPC B attachments in the same Transit Gateway route table.
Why wrong: Propagation would automatically add routes, potentially allowing direct communication.
- D
Add a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment.
This sends traffic destined to VPC B through VPC C.
- E
Create a VPC peering connection between VPC A and VPC B.
Why wrong: VPC peering would allow direct connectivity, bypassing the NVA.
Quick Answer
The correct actions are to add a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment, and to add a static route for VPC A's CIDR pointing to the VPC B attachment with a blackhole. This works because Transit Gateway static routes allow you to override dynamic propagation, forcing traffic through a Network Virtual Appliance (NVA) by directing the destination CIDR to the attachment of the inspection VPC, while the blackhole route prevents any direct path between the two VPCs. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of Transit Gateway route tables and how to enforce traffic inspection paths without relying on VPC peering or NAT instances. A common trap is forgetting that both a forward route (to the NVA) and a blackhole route (to block direct routing) are required; a single route alone will not prevent the Transit Gateway from using a more specific propagated route. Remember the memory tip: "Forward to inspect, blackhole to protect."
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 using AWS Transit Gateway to interconnect multiple VPCs and on-premises networks. The network engineer needs to ensure that traffic between VPC A and VPC B follows a specific path through a Network Virtual Appliance (NVA) in VPC C. Which TWO actions should the engineer take?
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
Add a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole.
Option B is correct because adding a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole forces traffic destined to VPC B to be dropped at the Transit Gateway, preventing direct routing. Option D is correct because adding a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment, ensures traffic from VPC A to VPC B is forwarded through the NVA in VPC C, enforcing the desired inspection path.
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.
- ✗
Associate VPC A's and VPC B's route tables with a different Transit Gateway route table that has a default route pointing to the VPC C attachment.
Why it's wrong here
This would affect all traffic, not just between A and B.
- ✓
Add a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole.
Why this is correct
This prevents VPC A from directly reaching VPC B via the Transit Gateway.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable route propagation for VPC A and VPC B attachments in the same Transit Gateway route table.
Why it's wrong here
Propagation would automatically add routes, potentially allowing direct communication.
- ✓
Add a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment.
Why this is correct
This sends traffic destined to VPC B through VPC C.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a VPC peering connection between VPC A and VPC B.
Why it's wrong here
VPC peering would allow direct connectivity, bypassing the NVA.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think enabling route propagation (Option C) is sufficient for traffic inspection, but it actually allows direct routing between VPCs, bypassing the NVA, unless specific static routes are added to override the propagated routes.
Detailed technical explanation
How to think about this question
Transit Gateway route tables support static routes and route propagation; by default, propagated routes from VPC attachments allow direct routing between VPCs. To force traffic through an NVA, you must override the propagated route with a more specific static route pointing to the NVA's attachment (VPC C), and optionally use a blackhole route to block direct paths. In real-world scenarios, this is common for centralized inspection of east-west traffic, where the NVA performs firewall or IDS/IPS functions, and the blackhole route prevents accidental direct connectivity if the NVA fails.
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
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: Add a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole. — Option B is correct because adding a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole forces traffic destined to VPC B to be dropped at the Transit Gateway, preventing direct routing. Option D is correct because adding a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment, ensures traffic from VPC A to VPC B is forwarded through the NVA in VPC C, enforcing the desired inspection path.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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