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Question 1,648 of 1,705

Network Design →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to place the bastion host in a public subnet with a security group that allows SSH only from the corporate IP range, and to configure the RDS database security group to allow MySQL access exclusively from the bastion host’s security group. This design achieves defense in depth by layering network controls: the bastion acts as a controlled entry point, while the database remains isolated in a private subnet with no direct internet exposure. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of security group chaining and least-privilege access for a secure bastion host for RDS maintenance. A common trap is to allow SSH from 0.0.0.0/0 or to use the same security group for both resources, which weakens isolation. Remember the mnemonic “Bastion blocks, database denies”—the bastion restricts who can enter, and the database restricts what can reach it.

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 has deployed an application in a VPC with public and private subnets. The application uses an Amazon RDS for MySQL database in a private subnet. To meet security requirements, the database must not be accessible from the internet. The application team needs to connect to the database for maintenance using SSH over a bastion host. Which architecture is the most secure?

Question 1hardmultiple choice

Review the full subnetting walkthrough →

A
Bastion host in a public subnet with the same security group as the database, allowing SSH from the corporate IP range and MySQL from the bastion
Why wrong: Using the same security group for both is less granular and not recommended.
B
Bastion host in a public subnet with a security group allowing SSH from 0.0.0.0/0, and database security group allowing MySQL from the bastion host's security group
Why wrong: Allowing SSH from 0.0.0.0/0 is insecure.
C
Connect to the database directly using a Site-to-Site VPN without a bastion host
Why wrong: While VPN is secure, the question specifies using SSH over a bastion host.
D
Bastion host in a public subnet with a security group allowing SSH from the corporate IP range, and database security group allowing MySQL from the bastion host's security group
This is secure and follows best practices.

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

✓

Bastion host in a public subnet with a security group allowing SSH from the corporate IP range, and database security group allowing MySQL from the bastion host's security group

A bastion host in a public subnet with a security group that allows SSH only from the corporate IP range, and the database security group allowing MySQL access only from the bastion host's security group, provides defense in depth. Using the same security group for both is less secure. Allowing SSH from anywhere (0.0.0.0/0) is insecure. A VPN provides secure access but is not always the simplest for maintenance; the bastion approach is common and secure when properly restricted.

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.

✗
Bastion host in a public subnet with the same security group as the database, allowing SSH from the corporate IP range and MySQL from the bastion
Why it's wrong here
Using the same security group for both is less granular and not recommended.
✗
Bastion host in a public subnet with a security group allowing SSH from 0.0.0.0/0, and database security group allowing MySQL from the bastion host's security group
Why it's wrong here
Allowing SSH from 0.0.0.0/0 is insecure.
✗
Connect to the database directly using a Site-to-Site VPN without a bastion host
Why it's wrong here
While VPN is secure, the question specifies using SSH over a bastion host.
✓
Bastion host in a public subnet with a security group allowing SSH from the corporate IP range, and database security group allowing MySQL from the bastion host's security group
Why this is correct
This is secure and follows best practices.
Related concept
CIDR notation defines the prefix length.

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

What is the correct answer to this question?

The correct answer is: Bastion host in a public subnet with a security group allowing SSH from the corporate IP range, and database security group allowing MySQL from the bastion host's security group — A bastion host in a public subnet with a security group that allows SSH only from the corporate IP range, and the database security group allowing MySQL access only from the bastion host's security group, provides defense in depth. Using the same security group for both is less secure. Allowing SSH from anywhere (0.0.0.0/0) is insecure. A VPN provides secure access but is not always the simplest for maintenance; the bastion approach is common and secure when properly restricted.

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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