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 to the VPC and allow resources in a private subnet to access the internet via IPv6. Which design should be used?
⚠ Common exam trap
It's easy for candidates to confuse the egress-only Internet Gateway with a NAT Gateway or assume that a standard Internet Gateway can be used for private subnets, not realizing that IPv6 requires a different outbound-only mechanism to maintain subnet privacy.
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
✓
Allocate an IPv6 CIDR block, create an egress-only Internet Gateway, and add a route to it from the private subnet.
An egress-only Internet Gateway (EIGW) is the correct AWS-managed service for enabling outbound-only IPv6 traffic from a VPC's private subnet to the internet, while preventing any unsolicited inbound connections. Unlike an Internet Gateway (IGW), which allows bidirectional traffic, an EIGW is specifically designed for IPv6 and ensures that resources in private subnets can initiate outbound connections without being directly reachable from the internet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Allocate an IPv6 CIDR block and add a route to an Internet Gateway from the private subnet.
Why it's wrong here
This would make the subnet public and allow inbound IPv6 traffic.
- ✗
Use a NAT instance with IPv6 support in a public subnet.
Why it's wrong here
NAT instances are not recommended and do not natively support IPv6.
- ✗
Allocate an IPv6 CIDR block and use a NAT Gateway for IPv6 traffic.
Why it's wrong here
NAT Gateway is for IPv4 only, not IPv6.
- ✓
Allocate an IPv6 CIDR block, create an egress-only Internet Gateway, and add a route to it from the private subnet.
Why this is correct
Egress-only IGW allows outbound IPv6 traffic but blocks inbound.
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1 more way this is tested on ANS-C01
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Variation 1. A company is designing a VPC with both IPv4 and IPv6 workloads. The VPC has an internet gateway, and the company wants to allow outbound IPv6 traffic to the internet from instances in a private subnet while blocking inbound IPv6 traffic from the internet. Which configuration should be used?
easy- A.Configure a security group that allows outbound traffic and denies inbound traffic.
- B.Configure a virtual private gateway and route traffic through it.
- ✓ C.Configure an egress-only internet gateway in the VPC and add a route for ::/0 to the egress-only internet gateway in the private subnet's route table.
- D.Configure a NAT gateway in a public subnet.
Why C: An egress-only internet gateway (EIGW) is a horizontally scaled, redundant component that allows outbound IPv6 traffic from instances in a private subnet to the internet, but prevents the internet from initiating an inbound IPv6 connection to those instances. By adding a default route (::/0) pointing to the EIGW in the private subnet's route table, outbound IPv6 traffic is forwarded to the internet gateway, while the EIGW inherently drops any unsolicited inbound IPv6 traffic. This meets the requirement exactly, as security groups and network ACLs alone cannot fully block inbound IPv6 from the internet when a standard internet gateway is used.
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.