- A
Associate an IPv6 CIDR block with the VPC and enable IPv6 on subnets.
Required for IPv6 functionality.
- B
Enable IPv6 support on the Transit Gateway and configure route tables to propagate IPv6 routes.
Transit Gateway must support IPv6 routing.
- C
Use VPC endpoints to route IPv6 traffic between VPCs.
Why wrong: VPC endpoints are for accessing specific services.
- D
Attach an egress-only internet gateway to the Transit Gateway.
Why wrong: Egress-only IGW is for internet access, not inter-VPC.
- E
Create a NAT gateway and attach it to the Transit Gateway.
Why wrong: NAT gateways do not support IPv6.
Question 1,350 of 1,705
How to Enable IPv6 Communication Between VPCs Using Transit Gateway
This ANS-C01 practice question tests your understanding of network design. 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 is designing a VPC with a CIDR block of 10.0.0.0/16. The VPC must support IPv6 and have subnets in three Availability Zones. The company plans to use an AWS Transit Gateway to connect multiple VPCs. Which TWO actions are required to enable IPv6 communication between VPCs through the Transit Gateway?
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
✓
Associate an IPv6 CIDR block with the VPC and enable IPv6 on subnets.
Option A is correct because to use IPv6 in a VPC, you must associate an IPv6 CIDR block (e.g., a /56 from Amazon's IPv6 pool) with the VPC and enable IPv6 on the subnets by assigning an IPv6 CIDR to each subnet. This ensures that resources in those subnets can have IPv6 addresses. Option B is also correct because to route IPv6 traffic between VPCs through a Transit Gateway, you need to configure the Transit Gateway route tables to include IPv6 routes. Transit Gateway supports IPv6 natively; there is no separate 'enable IPv6' setting, but the route tables must have entries for the IPv6 CIDRs of the attached VPCs. Without these routes, IPv6 packets will not be forwarded. Options C, D, and E are incorrect because VPC endpoints do not route traffic between VPCs, egress-only internet gateways only allow outbound IPv6 internet access, and NAT gateways are for IPv4 only.
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 an IPv6 CIDR block with the VPC and enable IPv6 on subnets.
Why this is correct
Required for IPv6 functionality.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Enable IPv6 support on the Transit Gateway and configure route tables to propagate IPv6 routes.
Why this is correct
Transit Gateway must support IPv6 routing.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use VPC endpoints to route IPv6 traffic between VPCs.
Why it's wrong here
VPC endpoints are for accessing specific services.
- ✗
Attach an egress-only internet gateway to the Transit Gateway.
Why it's wrong here
Egress-only IGW is for internet access, not inter-VPC.
- ✗
Create a NAT gateway and attach it to the Transit Gateway.
Why it's wrong here
NAT gateways do not support IPv6.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume Transit Gateway requires a special 'IPv6 enablement' setting or that NAT gateways or egress-only internet gateways are needed for IPv6 inter-VPC routing, when in fact IPv6 routing through Transit Gateway works identically to IPv4 routing—just with IPv6 routes in the route tables.
Detailed technical explanation
How to think about this question
When you associate an IPv6 CIDR block with a VPC, AWS automatically assigns a /56 IPv6 CIDR from the global unicast address range (2002::/16 for AWS-owned, or you can bring your own). Transit Gateway supports IPv6 traffic natively by forwarding packets based on destination IPv6 addresses in its route tables, but it does not require a separate 'enable IPv6' toggle; instead, you must add static routes or propagate routes from VPC route tables that include IPv6 destinations (e.g., ::/0 or specific IPv6 CIDRs). A common real-world scenario is connecting multiple VPCs with dual-stack subnets, where the Transit Gateway acts as a hub, and each VPC's route table must point to the Transit Gateway attachment for IPv6 traffic.
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 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: Associate an IPv6 CIDR block with the VPC and enable IPv6 on subnets. — Option A is correct because to use IPv6 in a VPC, you must associate an IPv6 CIDR block (e.g., a /56 from Amazon's IPv6 pool) with the VPC and enable IPv6 on the subnets by assigning an IPv6 CIDR to each subnet. This ensures that resources in those subnets can have IPv6 addresses. Option B is also correct because to route IPv6 traffic between VPCs through a Transit Gateway, you need to configure the Transit Gateway route tables to include IPv6 routes. Transit Gateway supports IPv6 natively; there is no separate 'enable IPv6' setting, but the route tables must have entries for the IPv6 CIDRs of the attached VPCs. Without these routes, IPv6 packets will not be forwarded. Options C, D, and E are incorrect because VPC endpoints do not route traffic between VPCs, egress-only internet gateways only allow outbound IPv6 internet access, and NAT gateways are for IPv4 only.
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: Jul 4, 2026
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