- A
Deploy a NAT gateway with an Elastic IP and route outbound traffic through it
A NAT gateway with an Elastic IP provides a single fixed IP for all outbound traffic from private instances, and no inbound traffic is allowed.
- B
Attach an Internet Gateway to the VPC and assign public IPs to the instances
Why wrong: Assigning public IPs would expose instances to inbound traffic and does not provide a fixed outbound IP because multiple instances would have different IPs.
- C
Place the instances behind an Application Load Balancer
Why wrong: An ALB handles inbound traffic, but outbound traffic from instances would still use the instance's own IP, which is not fixed.
- D
Create a VPC Gateway Endpoint for the partner's service
Why wrong: A Gateway Endpoint only supports AWS services like S3 and DynamoDB, not third-party partners.
Quick Answer
The correct answer is to deploy a NAT gateway with an Elastic IP and route outbound traffic through it. This design works because the NAT gateway, residing in a public subnet, performs source network address translation, mapping the private IPs of your EC2 instances to its own fixed Elastic IP address. This ensures the partner’s firewall sees a consistent source IP for all outbound traffic, while the instances remain in a private subnet with no direct inbound internet exposure. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how NAT gateways provide a static egress IP versus using a NAT instance or an internet gateway, which would expose instances. A common trap is choosing a NAT instance with an Elastic IP, but the gateway is fully managed, more scalable, and the preferred AWS service for this requirement. Memory tip: think “NAT Gateway = Fixed Egress, No Ingress” to recall that it provides a stable outbound IP while blocking unsolicited inbound connections.
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 migrating a legacy application to AWS. The application requires a fixed IP address for outbound traffic to a partner's firewall. The application will run on Amazon EC2 instances in a private subnet. Which design meets the requirement without exposing the instances to inbound internet traffic?
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
Deploy a NAT gateway with an Elastic IP and route outbound traffic through it
A NAT gateway with an Elastic IP provides a fixed public IP address for outbound traffic from instances in a private subnet while preventing any unsolicited inbound connections from the internet. The NAT gateway translates the private source IPs of the instances to its own Elastic IP, meeting the partner firewall's requirement for a fixed source IP without exposing the EC2 instances directly.
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.
- ✓
Deploy a NAT gateway with an Elastic IP and route outbound traffic through it
- ✗
Attach an Internet Gateway to the VPC and assign public IPs to the instances
Why it's wrong here
Assigning public IPs would expose instances to inbound traffic and does not provide a fixed outbound IP because multiple instances would have different IPs.
- ✗
Place the instances behind an Application Load Balancer
Why it's wrong here
An ALB handles inbound traffic, but outbound traffic from instances would still use the instance's own IP, which is not fixed.
- ✗
Create a VPC Gateway Endpoint for the partner's service
Why it's wrong here
A Gateway Endpoint only supports AWS services like S3 and DynamoDB, not third-party partners.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a NAT gateway with an Internet Gateway, thinking both provide outbound connectivity, but an Internet Gateway alone does not offer a fixed source IP for private instances and would expose them to inbound traffic if public IPs are assigned.
Detailed technical explanation
How to think about this question
A NAT gateway uses port address translation (PAT) to map multiple private IPs to a single Elastic IP, ensuring all outbound traffic appears to originate from that fixed IP. Unlike a NAT instance, the NAT gateway is managed by AWS and automatically scales up to 45 Gbps, handling failover across Availability Zones if deployed in each AZ. In scenarios where the partner firewall requires a specific source IP for logging or security rules, the NAT gateway's Elastic IP provides a stable, predictable address that does not change even if the underlying infrastructure is replaced.
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 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
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 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: Deploy a NAT gateway with an Elastic IP and route outbound traffic through it — A NAT gateway with an Elastic IP provides a fixed public IP address for outbound traffic from instances in a private subnet while preventing any unsolicited inbound connections from the internet. The NAT gateway translates the private source IPs of the instances to its own Elastic IP, meeting the partner firewall's requirement for a fixed source IP without exposing the EC2 instances directly.
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: Jun 24, 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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