- A
Create an egress-only internet gateway and add a route for ::/0 to it in the private subnet route tables.
An egress-only internet gateway allows outbound-only IPv6 traffic.
- B
Create an internet gateway and add a route for ::/0 to it in the private subnet route tables.
Why wrong: An internet gateway allows inbound IPv6 traffic, which violates the requirement.
- C
Allocate an IPv6 CIDR block to the VPC.
The VPC must have an IPv6 CIDR block to enable IPv6 communication.
- D
Create a NAT gateway in a public subnet.
Why wrong: NAT gateways only support IPv4 traffic.
- E
Configure a security group that allows outbound IPv6 traffic.
Why wrong: Security groups control traffic but are not a substitute for a gateway.
Question 44 of 1,705
Setting Up Outbound IPv6 Access for Private Subnets with Egress-Only IGW
This ANS-C01 practice question tests your understanding of network design. 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 an IPv4 CIDR block of 10.0.0.0/16. They have subnets in three Availability Zones. They need to add IPv6 connectivity to the VPC and allow instances in private subnets to initiate outbound IPv6 connections to the internet, but not allow inbound connections from the internet. Which TWO actions must be taken?
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
✓
Create an egress-only internet gateway and add a route for ::/0 to it in the private subnet route tables.
Option A is correct because an egress-only internet gateway (EIGW) is a horizontally scaled, redundant component that allows outbound IPv6 traffic from instances in private subnets to the internet, while preventing inbound connections initiated from the internet. Adding a route for ::/0 to the EIGW in the private subnet route tables enables this outbound-only IPv6 connectivity. Option C is correct because the VPC must have an associated IPv6 CIDR block (allocated from Amazon's pool or a BYOIP range) before any IPv6 routing or gateway functionality can be used.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create an egress-only internet gateway and add a route for ::/0 to it in the private subnet route tables.
Why this is correct
An egress-only internet gateway allows outbound-only IPv6 traffic.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create an internet gateway and add a route for ::/0 to it in the private subnet route tables.
Why it's wrong here
An internet gateway allows inbound IPv6 traffic, which violates the requirement.
- ✓
Allocate an IPv6 CIDR block to the VPC.
Why this is correct
The VPC must have an IPv6 CIDR block to enable IPv6 communication.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a NAT gateway in a public subnet.
Why it's wrong here
NAT gateways only support IPv4 traffic.
- ✗
Configure a security group that allows outbound IPv6 traffic.
Why it's wrong here
Security groups control traffic but are not a substitute for a gateway.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the distinction between an egress-only internet gateway (for outbound-only IPv6) and an internet gateway (for bidirectional IPv6), and the trap here is that candidates assume a NAT gateway or security group rules can substitute for the correct gateway type, ignoring that NAT gateways are IPv4-only and security groups are stateful and do not control inbound internet access at the routing layer.
Detailed technical explanation
How to think about this question
An egress-only internet gateway works only with IPv6 traffic and uses a static one-way translation: it forwards packets from the VPC to the internet but drops any unsolicited inbound packets. Under the hood, the EIGW is implemented as a virtual appliance that performs destination-based routing without maintaining connection state, relying on the route table's ::/0 entry to direct outbound traffic. In a real-world scenario, if you mistakenly use an IGW for private subnets, instances become reachable from the internet via their IPv6 addresses, creating a security risk that an EIGW explicitly avoids.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create an egress-only internet gateway and add a route for ::/0 to it in the private subnet route tables. — Option A is correct because an egress-only internet gateway (EIGW) is a horizontally scaled, redundant component that allows outbound IPv6 traffic from instances in private subnets to the internet, while preventing inbound connections initiated from the internet. Adding a route for ::/0 to the EIGW in the private subnet route tables enables this outbound-only IPv6 connectivity. Option C is correct because the VPC must have an associated IPv6 CIDR block (allocated from Amazon's pool or a BYOIP range) before any IPv6 routing or gateway functionality can be used.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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