- A
Deploy a NAT instance in a private subnet and add a default route to the NAT instance in the private subnet's route table.
Why wrong: Incorrect. A NAT instance in a private subnet is used to provide outbound internet access for instances in private subnets, not public subnets. Moreover, the default route should be in the private subnet's route table, not the public subnet's.
- B
Deploy an Application Load Balancer (ALB) in a public subnet and route outbound traffic through the ALB.
Why wrong: Incorrect. An Application Load Balancer (ALB) is used for load balancing HTTP/HTTPS traffic, not for routing outbound internet traffic.
- C
Attach an Internet Gateway to the VPC and add a default route to the Internet Gateway in the public subnet's route table.
Correct. An Internet Gateway attached to the VPC and a default route to the IGW in the public subnet's route table allows instances in public subnets to initiate outbound connections to the internet. To prevent direct inbound access, security groups must be configured to block such traffic.
- D
Deploy a NAT Gateway in a public subnet and add a default route to the NAT Gateway in the private subnet's route table.
Why wrong: Incorrect. A NAT Gateway in a public subnet is used to provide outbound internet access for instances in private subnets. Since the web servers are in public subnets, a NAT Gateway is unnecessary; they can use the Internet Gateway directly. Additionally, the default route should be in the public subnet's route table, not the private subnet's.
Configuring NAT Gateway for Outbound-Only Internet Access in Private Subnets
This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: internet Gateway (IGW). 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 deploying a multi-tier web application in a VPC with public and private subnets. The web servers in the public subnets must be able to initiate outbound connections to the internet for software updates, but must not be directly accessible from the internet. Which configuration meets these requirements?
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
Attach an Internet Gateway to the VPC and add a default route to the Internet Gateway in the public subnet's route table.
For instances in public subnets, outbound internet access is provided by attaching an Internet Gateway (IGW) to the VPC and adding a default route to the IGW in the public subnet's route table. To prevent direct inbound access, you use security groups or network ACLs to block incoming traffic. Option C correctly describes this configuration. Option D is for private subnets, where instances need a NAT Gateway for outbound access and must not have public IPs, which contradicts the stem stating the web servers are in public subnets. Options A and B are incorrect because NAT instances and ALBs are not used for providing outbound internet access from public subnets directly.
Key principle: Internet Gateway (IGW)
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Deploy a NAT instance in a private subnet and add a default route to the NAT instance in the private subnet's route table.
Why it's wrong here
Incorrect. A NAT instance in a private subnet is used to provide outbound internet access for instances in private subnets, not public subnets. Moreover, the default route should be in the private subnet's route table, not the public subnet's.
- ✗
Deploy an Application Load Balancer (ALB) in a public subnet and route outbound traffic through the ALB.
Why it's wrong here
Incorrect. An Application Load Balancer (ALB) is used for load balancing HTTP/HTTPS traffic, not for routing outbound internet traffic.
- ✓
Attach an Internet Gateway to the VPC and add a default route to the Internet Gateway in the public subnet's route table.
Why this is correct
Correct. An Internet Gateway attached to the VPC and a default route to the IGW in the public subnet's route table allows instances in public subnets to initiate outbound connections to the internet. To prevent direct inbound access, security groups must be configured to block such traffic.
Related concept
Internet Gateway (IGW)
- ✗
Deploy a NAT Gateway in a public subnet and add a default route to the NAT Gateway in the private subnet's route table.
Why it's wrong here
Incorrect. A NAT Gateway in a public subnet is used to provide outbound internet access for instances in private subnets. Since the web servers are in public subnets, a NAT Gateway is unnecessary; they can use the Internet Gateway directly. Additionally, the default route should be in the public subnet's route table, not the private subnet's.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that candidates often assume that to prevent direct inbound access, instances must be in private subnets and thus select a NAT Gateway. However, the question explicitly states the web servers are in public subnets, so an Internet Gateway is the correct component for outbound access, and inbound blocking is done via security groups, not by using NAT.
Detailed technical explanation
How to think about this question
A NAT Gateway uses source network address translation (SNAT) to map private IP addresses of instances in private subnets to its own Elastic IP address for outbound traffic, while dropping any unsolicited inbound traffic. Unlike a NAT instance, a NAT Gateway is a managed service that automatically scales up to 45 Gbps and does not require patching or failover scripts. In real-world scenarios, this configuration is common for multi-tier applications where web servers need to fetch updates from repositories like yum or apt without exposing them to direct internet access.
KKey Concepts to Remember
- Internet Gateway (IGW)
- Public Subnet
- Security Group
- Default Route
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
Internet Gateway (IGW)
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Internet Gateway (IGW).
What is the correct answer to this question?
The correct answer is: Attach an Internet Gateway to the VPC and add a default route to the Internet Gateway in the public subnet's route table. — For instances in public subnets, outbound internet access is provided by attaching an Internet Gateway (IGW) to the VPC and adding a default route to the IGW in the public subnet's route table. To prevent direct inbound access, you use security groups or network ACLs to block incoming traffic. Option C correctly describes this configuration. Option D is for private subnets, where instances need a NAT Gateway for outbound access and must not have public IPs, which contradicts the stem stating the web servers are in public subnets. Options A and B are incorrect because NAT instances and ALBs are not used for providing outbound internet access from public subnets directly.
What should I do if I get this ANS-C01 question wrong?
Review internet Gateway (IGW), then practise related ANS-C01 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Internet Gateway (IGW)
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Last reviewed: Jul 4, 2026
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