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Network Design →easyMultiple ChoiceObjective-mapped

ANS-C01 Network Design Practice Question

This ANS-C01 practice question tests your understanding of network design. 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. 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 wants to provide internet access to instances in a private subnet without using a NAT Gateway, due to cost constraints. They have a public subnet with a bastion host that has a public IP. They also have a VPC with an Internet Gateway. What is the most cost-effective way to allow outbound internet access for instances in the private subnet?

A
Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance.
NAT instance is a cost-effective alternative to NAT Gateway.
B
Use a VPN connection to a third-party internet proxy.
Why wrong: VPN is costly and adds complexity.
C
Create a VPC endpoint for Amazon S3 and configure the private subnet to use it.
Why wrong: VPC endpoint only provides access to specific AWS services, not the internet.
D
Configure the bastion host as a NAT instance by enabling IP forwarding.
Why wrong: Bastion host is for management, not for NAT; but could be used if configured, but usually not recommended.

Full breakdown with real-world context →

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

✓

Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance.

The correct answer is A: Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance. A NAT instance is a cost-effective alternative to NAT Gateway, as it uses an EC2 instance with IP forwarding enabled and can be run on a low-cost instance type. It requires management but avoids NAT Gateway hourly charges. Option B is incorrect because a VPN connection to a third-party proxy introduces unnecessary complexity and cost. Option C is incorrect because VPC endpoints only provide access to specific AWS services (e.g., S3), not general internet access. Option D is incorrect because the bastion host is typically used for SSH access, and while it could be configured for NAT, it is not recommended for security reasons; a dedicated NAT instance in a public subnet is the proper approach.

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

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance.
Why this is correct
NAT instance is a cost-effective alternative to NAT Gateway.
Related concept
CIDR notation defines the prefix length.
✗
Use a VPN connection to a third-party internet proxy.
Why it's wrong here
VPN is costly and adds complexity.
✗
Create a VPC endpoint for Amazon S3 and configure the private subnet to use it.
Why it's wrong here
VPC endpoint only provides access to specific AWS services, not the internet.
✗
Configure the bastion host as a NAT instance by enabling IP forwarding.
Why it's wrong here
Bastion host is for management, not for NAT; but could be used if configured, but usually not recommended.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

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

How to think about this question

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.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

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

How this comes up in practice

A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.

Visual reference

Quick reference

AWS S3 Storage Class Comparison

Storage Class	Min Duration	Retrieval	Use Case
S3 Standard	None	Immediate	Frequently accessed data
S3 Standard-IA	30 days	Immediate	Infrequent access, rapid retrieval
S3 One Zone-IA	30 days	Immediate	Non-critical infrequent data
S3 Intelligent-Tiering	None	Immediate–hours	Unknown or changing access patterns
S3 Glacier Instant	90 days	Milliseconds	Archive with instant retrieval
S3 Glacier Flexible	90 days	Minutes–hours	Archive, flexible retrieval
S3 Glacier Deep Archive	180 days	Hours	Long-term compliance archive

What to study next

Got this wrong? Here's your next step.

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

Questions learners often ask

What does this ANS-C01 question test?

Network Design — This question tests Network Design — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance. — The correct answer is A: Launch a NAT instance in the public subnet and configure the private subnet route table to point 0.0.0.0/0 to the NAT instance. A NAT instance is a cost-effective alternative to NAT Gateway, as it uses an EC2 instance with IP forwarding enabled and can be run on a low-cost instance type. It requires management but avoids NAT Gateway hourly charges. Option B is incorrect because a VPN connection to a third-party proxy introduces unnecessary complexity and cost. Option C is incorrect because VPC endpoints only provide access to specific AWS services (e.g., S3), not general internet access. Option D is incorrect because the bastion host is typically used for SSH access, and while it could be configured for NAT, it is not recommended for security reasons; a dedicated NAT instance in a public subnet is the proper approach.

What should I do if I get this ANS-C01 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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