ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
Many 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.
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.
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.
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.
- ✓
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.