ANS-C01 Network Design Practice Question
A company has a VPC with an IPv4 CIDR block of 10.0.0.0/16. They need to add IPv6 connectivity for their internet-facing applications. The VPC currently has an internet gateway attached. What is the MOST efficient way to enable IPv6?
⚠ Common exam trap
AWS often tests the misconception that an egress-only internet gateway is required for all IPv6 traffic, but the trap here is that an egress-only internet gateway is only for outbound-only scenarios, whereas internet-facing applications need bidirectional IPv6 traffic, which requires a standard internet 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
✓
Assign an Amazon-provided IPv6 CIDR block to the VPC and subnets, and update route tables to use an internet gateway for IPv6
The most efficient way to enable IPv6 for an existing VPC with an internet gateway is to request an Amazon-provided IPv6 CIDR block (a /56 block) for the VPC, assign a /64 IPv6 CIDR to each subnet, and then update the route tables to direct ::/0 traffic to the internet gateway. The internet gateway is a dual-stack resource that inherently supports both IPv4 and IPv6 traffic, so no additional gateway is needed for outbound-only or inbound IPv6 connectivity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Assign an Amazon-provided IPv6 CIDR block to the VPC and subnets, and update route tables to use an internet gateway for IPv6
Why this is correct
The internet gateway supports both IPv4 and IPv6; route tables can direct IPv6 traffic to it.
- ✗
Create a transit gateway and attach the VPC, then route IPv6 traffic through a VPN
Why it's wrong here
Transit gateway is not needed for internet connectivity.
- ✗
Create a NAT Gateway in a public subnet and route IPv6 traffic through it
Why it's wrong here
NAT Gateways are for IPv4 only.
- ✗
Assign an IPv6 CIDR to the VPC and subnets, and add an egress-only internet gateway
Why it's wrong here
Egress-only internet gateway is for outbound only; internet-facing apps need inbound.
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Same concept, more angles
1 more way 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 designing a VPC with both IPv4 and IPv6 CIDR blocks. The VPC must support internet-facing applications accessible via IPv6. Which resource must be configured as IPv6-enabled to allow internet traffic?
easy- ✓ A.Internet Gateway
- B.VPC Peering connection
- C.NAT Gateway
- D.Transit Gateway
Why A: An Internet Gateway (IGW) is the only resource that supports both IPv4 and IPv6 traffic and provides a target in the VPC route table for IPv6 default routes (::/0) to enable direct internet access for IPv6-enabled resources. Unlike IPv4, which often requires NAT for private addressing, IPv6 globally unique addresses allow direct communication through the IGW without translation.
JA
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.