- A
Use network ACLs on the transit gateway attachments to filter traffic.
Why wrong: Transit gateway does not support network ACLs on attachments.
- B
Use security groups on the VPC attachments to allow or deny traffic.
Why wrong: Security groups are per-ENI, not at transit gateway level.
- C
Create separate transit gateway route tables for each VPC and add only the desired routes for other VPCs.
Enables selective communication.
- D
Create a single transit gateway route table and associate all VPC attachments with it.
Why wrong: Would allow all-to-all communication.
Question 668 of 1,705
Transit Gateway Route Table Isolation for VPC Traffic Control — AWS Advanced Networking Specialty Explained
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. 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 multiple VPCs connected via AWS Transit Gateway. Each VPC has its own route table in the transit gateway. The company wants to restrict traffic between certain VPCs. For example, VPC A should be able to send traffic to VPC B but not to VPC C. VPC B should be able to send traffic to VPC C. Which configuration should the company use?
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
✓
Create separate transit gateway route tables for each VPC and add only the desired routes for other VPCs.
Option C is correct because AWS Transit Gateway supports multiple route tables, and by creating a separate route table for each VPC attachment, you can control which VPCs can communicate by selectively adding routes to the desired destination VPC CIDRs. This allows VPC A to have a route only to VPC B, while VPC B's route table includes routes to both VPC A and VPC C, achieving the required traffic isolation without relying on stateful or stateless filtering at the attachment level.
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.
- ✗
Use network ACLs on the transit gateway attachments to filter traffic.
Why it's wrong here
Transit gateway does not support network ACLs on attachments.
- ✗
Use security groups on the VPC attachments to allow or deny traffic.
Why it's wrong here
Security groups are per-ENI, not at transit gateway level.
- ✓
Create separate transit gateway route tables for each VPC and add only the desired routes for other VPCs.
Why this is correct
Enables selective communication.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a single transit gateway route table and associate all VPC attachments with it.
Why it's wrong here
Would allow all-to-all communication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Transit Gateway route tables with VPC route tables or assume that security groups or network ACLs can be applied to Transit Gateway attachments, when in fact route table isolation is the only native mechanism for controlling inter-VPC traffic at the Transit Gateway level.
Detailed technical explanation
How to think about this question
Transit Gateway route tables use route propagation and static routes to control inter-VPC traffic; each attachment can be associated with exactly one route table, and route tables can be isolated by not propagating routes from certain attachments. Under the hood, the Transit Gateway evaluates the route table associated with the source attachment to determine the next hop, and the destination attachment must also have a route back to the source for bidirectional communication. In a real-world scenario, this design is critical for hub-and-spoke or shared service VPC architectures where you need to enforce strict traffic segmentation, such as preventing a development VPC from accessing a production VPC while allowing both to reach a shared services VPC.
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.
Visual reference
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: Create separate transit gateway route tables for each VPC and add only the desired routes for other VPCs. — Option C is correct because AWS Transit Gateway supports multiple route tables, and by creating a separate route table for each VPC attachment, you can control which VPCs can communicate by selectively adding routes to the desired destination VPC CIDRs. This allows VPC A to have a route only to VPC B, while VPC B's route table includes routes to both VPC A and VPC C, achieving the required traffic isolation without relying on stateful or stateless filtering at the attachment level.
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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Same concept, more angles
2 more ways this is tested on ANS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is using AWS Transit Gateway to connect multiple VPCs and on-premises networks via Direct Connect and Site-to-Site VPN. The network team wants to ensure that traffic between VPCs does not traverse the on-premises network. Which Transit Gateway feature should be used?
medium- A.Transit Gateway Multicast
- B.Transit Gateway Network Manager
- C.Transit Gateway BGP over AWS Direct Connect
- ✓ D.Transit Gateway route tables with separate associations and propagations
Why D: Transit Gateway route tables with separate associations and propagations allow you to isolate traffic between VPCs and on-premises networks. By associating VPC attachments to one route table and on-premises attachments (Direct Connect, VPN) to another, you can prevent VPC-to-VPC traffic from being routed through the on-premises network. This ensures that inter-VPC traffic stays within AWS, meeting the requirement.
Variation 2. A company is using AWS Transit Gateway to connect multiple VPCs and an on-premises network via Direct Connect. The network team wants to isolate traffic between VPCs while allowing all VPCs to reach the on-premises network. Which TWO configurations should be implemented?
medium- A.Attach the Direct Connect virtual interface to a VPN attachment on the Transit Gateway
- B.Use a Direct Connect gateway to propagate routes to all VPCs
- ✓ C.Create separate Transit Gateway route tables for each VPC and associate them with the respective VPC attachments
- D.Use a single Transit Gateway route table for all attachments
- E.Create VPC peering connections between each VPC
Why C: Option C is correct because creating separate Transit Gateway route tables for each VPC and associating them with the respective VPC attachments enforces traffic isolation between VPCs: each VPC route table only contains routes to the on-premises network, not to other VPCs, thus achieving the isolation requirement. Option A is incorrect because a Direct Connect virtual interface must be attached to a Direct Connect Gateway, which then associates with the Transit Gateway via a Transit Gateway association. The VPN attachment is for VPN connections, not Direct Connect. Therefore, only Option C meets the isolation requirement.
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Last reviewed: Jul 4, 2026
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