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Network Security, Compliance and Governance →mediumMultiple ChoiceObjective-mapped

ANS-C01 Network Security, Compliance and Governance Practice Question

This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 wants to allow an external auditor to access a specific EC2 instance in their VPC for a limited time. The auditor will connect via SSH from a known IP address. What is the MOST secure way to grant access?

A
Assign a public IP to the instance and create a security group rule allowing SSH from the auditor's IP.
Why wrong: Assigning a public IP to the instance and creating a security group rule allowing SSH from the auditor's IP is somewhat secure but still exposes the instance directly to the internet, increasing attack surface compared to a bastion host that can be hardened and monitored separately.
B
Configure a security group for the instance that allows SSH from the VPC CIDR.
Why wrong: Configuring a security group that allows SSH from the VPC CIDR is insecure because any compromised resource within the VPC could access the instance, violating the principle of least privilege.
C
Create a bastion host in a public subnet with a security group allowing SSH from the auditor's IP, and allow SSH from the bastion to the instance.
Creating a bastion host in a public subnet with a security group allowing SSH from the auditor's IP, and allowing SSH from the bastion to the instance, is the most secure option. It provides a controlled, auditable entry point and minimizes the attack surface of the target instance.
D
Set up a client VPN endpoint and allow the auditor to connect to the VPC, then SSH to the instance.
Why wrong: Setting up a client VPN endpoint and allowing the auditor to connect to the VPC then SSH to the instance is secure but adds complexity and cost. For a temporary, single-instance audit, a bastion host is simpler and equally secure.

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

✓

Create a bastion host in a public subnet with a security group allowing SSH from the auditor's IP, and allow SSH from the bastion to the instance.

The most secure approach is to use a bastion host (jump box) in a public subnet. The bastion host's security group restricts SSH access to only the auditor's known IP address. The target EC2 instance's security group allows SSH only from the bastion host's private IP, minimizing direct exposure. Option A (assigning a public IP to the instance) exposes the instance directly to the internet, even with a restricted security group, increasing attack surface. Option B (allowing SSH from the entire VPC CIDR) is insecure because any compromised resource within the VPC could access the instance. Option D (client VPN) is secure but adds complexity and cost for a temporary single-instance access; the bastion host is simpler and more direct.

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.

✗
Assign a public IP to the instance and create a security group rule allowing SSH from the auditor's IP.
Why it's wrong here
Assigning a public IP to the instance and creating a security group rule allowing SSH from the auditor's IP is somewhat secure but still exposes the instance directly to the internet, increasing attack surface compared to a bastion host that can be hardened and monitored separately.
✗
Configure a security group for the instance that allows SSH from the VPC CIDR.
Why it's wrong here
Configuring a security group that allows SSH from the VPC CIDR is insecure because any compromised resource within the VPC could access the instance, violating the principle of least privilege.
✓
Create a bastion host in a public subnet with a security group allowing SSH from the auditor's IP, and allow SSH from the bastion to the instance.
Why this is correct
Creating a bastion host in a public subnet with a security group allowing SSH from the auditor's IP, and allowing SSH from the bastion to the instance, is the most secure option. It provides a controlled, auditable entry point and minimizes the attack surface of the target instance.
Related concept
CIDR notation defines the prefix length.
✗
Set up a client VPN endpoint and allow the auditor to connect to the VPC, then SSH to the instance.
Why it's wrong here
Setting up a client VPN endpoint and allowing the auditor to connect to the VPC then SSH to the instance is secure but adds complexity and cost. For a temporary, single-instance audit, a bastion host is simpler and equally secure.

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

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 Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Create a bastion host in a public subnet with a security group allowing SSH from the auditor's IP, and allow SSH from the bastion to the instance. — The most secure approach is to use a bastion host (jump box) in a public subnet. The bastion host's security group restricts SSH access to only the auditor's known IP address. The target EC2 instance's security group allows SSH only from the bastion host's private IP, minimizing direct exposure. Option A (assigning a public IP to the instance) exposes the instance directly to the internet, even with a restricted security group, increasing attack surface. Option B (allowing SSH from the entire VPC CIDR) is insecure because any compromised resource within the VPC could access the instance. Option D (client VPN) is secure but adds complexity and cost for a temporary single-instance access; the bastion host is simpler and more direct.

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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