Amazon ANS-C01 Exam - Topic 1 Question 64 Discussion

Actual exam question for Amazon's ANS-C01 exam

Question #: 64
Topic #: 1

A company has multiple VPCs with subnets that use IPv4. Traffic from the VPCs to the internet uses a NAT gateway. The company wants to transition to IPv6.

A network engineer creates multiple IPv6-only subnets in an existing testing VPC. The network engineer deploys a new Amazon EC2 instance that has an IPv6 address into one of the subnets. During testing, the network engineer discovers that the new EC2 instance is not able to communicate with an IPv4-only service through the internet. The network engineer needs to enable the IPv6 EC2 instance to communicate with the IPv4-only service.

Which solution will meet this requirement?

AEnable DNS64 for the IPv6-only subnets. Update the route tables for the IPv6-only subnets to send traffic through the NAT gateway.

BEnable NAT64 for the testing VPC. Reconfigure the existing NAT gateway to support IPv6.

CEnable DNS64 for the new EC2 instance. Create a new egress-only internet gateway that supports IPv6.

DEnable NAT64 for each route table. Create a new NAT gateway that supports both IPv4 and IPv6.

Show Suggested Answer

Suggested Answer: A

Understanding the Issue: The IPv6-only EC2 instance cannot communicate with IPv4-only services because IPv6 and IPv4 are not directly compatible. To bridge this gap, DNS64 and NAT64 are used together. However, AWS NAT gateways do not natively support NAT64, but you can use DNS64 to translate IPv4 DNS records (A records) into IPv6-compatible addresses (AAAA records).

DNS64 for IPv6-Only Subnets: DNS64 is a service that synthesizes AAAA records for IPv4-only services. This allows IPv6-only clients to resolve IPv4 addresses as IPv6-compatible addresses, enabling communication through the NAT gateway.

NAT Gateway with Route Table Updates: The NAT gateway enables outbound communication from private subnets to the internet. Updating the route tables for IPv6-only subnets to send traffic through the NAT gateway ensures that the IPv6 EC2 instance can reach IPv4 services.

by Brent at May 04, 2026, 02:11 PM

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