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Question 32 of 1,705

Network Security, Compliance and Governance →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to create a bastion host in a public subnet with a security group allowing SSH from the auditor’s known IP, and allow SSH from the bastion to the target instance. This is the most secure approach because it enforces a two-layer security group restriction: the bastion’s inbound rule limits access to a single, verified source IP, while the instance’s inbound rule only trusts the bastion’s private IP, eliminating direct exposure. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of layered security and temporary access patterns, often appearing in questions about audit or third-party connectivity. A common trap is selecting a VPN or wide CIDR rule, but the key is that a bastion host with strict source IP restrictions provides the narrowest attack surface for temporary SSH access. Memory tip: think “two doors, one key”—the bastion is the only door the auditor can knock on, and the instance only opens for the bastion.

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?

Question 1mediummultiple choice

Full question →

A
Assign a public IP to the instance and create a security group rule allowing SSH from the auditor's IP.
Why wrong: Directly exposing the instance to the internet increases attack surface, even with IP restriction.
B
Configure a security group for the instance that allows SSH from the VPC CIDR.
Why wrong: This allows SSH from any instance in the VPC, which is too permissive.
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.
The bastion acts as a jump box, limiting exposure and providing a single point of access.
D
Set up a client VPN endpoint and allow the auditor to connect to the VPC, then SSH to the instance.
Why wrong: While more secure than direct internet access, it is more complex and the instance is still accessible from the entire VPC network.

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.

Option B is correct because using a bastion host with a security group that restricts the source IP is a secure practice. Option A is wrong because opening port 22 to 0.0.0.0/0 is insecure. Option C is wrong because a VPN still exposes the instance to the VPC network. Option D is wrong because a security group with a wide CIDR is less restrictive.

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
Directly exposing the instance to the internet increases attack surface, even with IP restriction.
✗
Configure a security group for the instance that allows SSH from the VPC CIDR.
Why it's wrong here
This allows SSH from any instance in the VPC, which is too permissive.
✓
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
The bastion acts as a jump box, limiting exposure and providing a single point of access.
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
While more secure than direct internet access, it is more complex and the instance is still accessible from the entire VPC network.

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 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.

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. — Option B is correct because using a bastion host with a security group that restricts the source IP is a secure practice. Option A is wrong because opening port 22 to 0.0.0.0/0 is insecure. Option C is wrong because a VPN still exposes the instance to the VPC network. Option D is wrong because a security group with a wide CIDR is less restrictive.

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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