Quick Answer
The answer is an egress-only internet gateway, which is the correct choice because it enables outbound IPv6 traffic from private subnets to the internet while explicitly blocking any unsolicited inbound IPv6 connections. Unlike a standard internet gateway, which allows bidirectional traffic, an egress-only internet gateway operates at the IPv6 layer as a stateful device that only forwards packets originating from within the VPC, making it the only AWS resource designed for this specific use case. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of IPv6 routing distinctions and the limitations of NAT gateways, which are IPv4-only and cannot handle IPv6 traffic. A common trap is confusing the egress-only internet gateway with a NAT gateway or assuming an internet gateway works for outbound-only IPv6 traffic; remember that an internet gateway permits inbound traffic by default, breaking the private subnet requirement. Memory tip: think “EIG for IPv6 out, no in”—just like a one-way valve for egress-only internet gateway traffic.
This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 has a VPC with both IPv4 and IPv6 CIDRs. They need to allow outbound IPv6 traffic from private subnets to the internet. What should they use?
An internet gateway attached to the VPC.
Why wrong: Internet gateway allows bidirectional traffic, which may pose security risk.
A customer-managed prefix list.
Why wrong: Prefix list is for IP address grouping, not for internet access.
A NAT gateway in a public subnet.
Why wrong: NAT gateway does not support IPv6.
An egress-only internet gateway.
Designed for outbound-only IPv6 traffic from private subnets.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
An egress-only internet gateway.
Option B is correct because an egress-only internet gateway allows outbound IPv6 traffic from private subnets while preventing inbound traffic. Option A is wrong because NAT gateway is for IPv4 only. Option C is wrong because internet gateway allows inbound traffic. Option D is wrong because the prefix list is for route targets, not a device.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
An internet gateway attached to the VPC.
Why it's wrong here
Internet gateway allows bidirectional traffic, which may pose security risk.
A customer-managed prefix list.
Why it's wrong here
Prefix list is for IP address grouping, not for internet access.
A NAT gateway in a public subnet.
An egress-only internet gateway.
Why this is correct
Designed for outbound-only IPv6 traffic from private subnets.
Related concept
CIDR notation defines the prefix length.
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
The correct answer is: An egress-only internet gateway. — Option B is correct because an egress-only internet gateway allows outbound IPv6 traffic from private subnets while preventing inbound traffic. Option A is wrong because NAT gateway is for IPv4 only. Option C is wrong because internet gateway allows inbound traffic. Option D is wrong because the prefix list is for route targets, not a device.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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.
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