The answer is a NAT Gateway and an Egress-only Internet Gateway. Both options provide outbound internet access for private subnets while preventing unsolicited inbound connections, but they operate at different protocol layers. A NAT Gateway, deployed in a public subnet with an Elastic IP, translates private IPv4 addresses for outbound traffic and drops any inbound traffic not part of an established session. An Egress-only Internet Gateway serves the same purpose for IPv6 traffic, allowing outbound-only communication by design, as it is a stateful gateway that forwards traffic only from the VPC to the internet. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of how to architect secure outbound connectivity without exposing private resources—a common trap is confusing a NAT Gateway with a NAT instance or assuming an Internet Gateway alone provides outbound-only access. Remember: NAT Gateway for IPv4, Egress-only for IPv6; both are outbound-only, but the Egress-only Gateway is simpler because it requires no NAT translation.
ANS-C01 Network Design Practice Question
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 is designing a VPC with a public subnet and a private subnet. The private subnet instances need to access the internet for software updates. Which TWO options allow outbound internet access while preventing inbound connections? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
NAT Gateway in the public subnet
A NATGateway in the public subnet allows instances in the private subnet to initiate outbound connections to the internet (e.g., for software updates) while preventing any unsolicited inbound connections from the internet. The NAT Gateway translates the private IP addresses of the instances to its own Elastic IP address, and because it does not maintain state for inbound traffic that was not initiated from within the VPC, it blocks all inbound connection attempts.
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.
✓
NAT Gateway in the public subnet
Why this is correct
Allows outbound IPv4 traffic from private subnet.
Related concept
Read the scenario before looking for a memorised answer.
✓
Egress-only Internet Gateway
Why this is correct
Allows outbound IPv6 traffic only.
Related concept
Read the scenario before looking for a memorised answer.
VPC Peering connection to a VPC with internet access
Why it's wrong here
VPC Peering does not provide internet access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse an Egress-Only Internet Gateway with a NAT Gateway, not realizing that the Egress-Only Internet Gateway is exclusively for IPv6 traffic and does not support IPv4, which is the typical protocol for software updates.
Detailed technical explanation
How to think about this question
Under the hood, a NATGateway uses Port Address Translation (PAT) to map multiple private IP addresses to a single Elastic IP address, tracking each session in a connection table. A subtle behavior is that a NAT Gateway cannot be used by instances in the same subnet as the gateway; it must reside in a public subnet with a route to an Internet Gateway, while private subnet route tables point 0.0.0.0/0 to the NAT Gateway. In a real-world scenario, if you need to update thousands of instances simultaneously, a single NAT Gateway can become a bottleneck, so you might deploy multiple NAT Gateways across Availability Zones for high availability and throughput.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: NAT Gateway in the public subnet — A NAT Gateway in the public subnet allows instances in the private subnet to initiate outbound connections to the internet (e.g., for software updates) while preventing any unsolicited inbound connections from the internet. The NAT Gateway translates the private IP addresses of the instances to its own Elastic IP address, and because it does not maintain state for inbound traffic that was not initiated from within the VPC, it blocks all inbound connection attempts.
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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Question Discussion
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