This ANS-C01 practice question tests your understanding of network implementation. 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 designing a VPC with a public subnet and a private subnet. The private subnet hosts an RDS database, and the public subnet hosts a web server. The web server needs to access the database. Which TWO of the following are required to allow the web server to connect to the database?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An inbound rule in the database's security group that references the web server's security group.
Option B is correct because a security group on the database must allow inbound traffic from the web server's security group. Option D is correct because the private subnet route table does not need a route to the internet gateway, but it must have a route to the NAT gateway or VPC peering if needed, but for database access, no route to internet is needed. However, the question asks for required components. Actually, to allow the web server to connect to the database, you need a security group rule on the database allowing the web server's security group, and you need the private subnet to have a route to the public subnet's CIDR via the local route (already present). So the correct options are B and C? Wait, let's analyze: A is not required because you can use security group IDs. B is required. C is required because the private subnet must have a route to the public subnet's CIDR (which is local and automatically added). D is not required because internet gateway is not needed for private subnet to communicate within VPC. E is not required because NAT gateway is for internet access. So the two correct are B and C. But C says "A route table associated with the private subnet that includes a route to the internet gateway" which is wrong. I need to correct the options. Let me rephrase:
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.
✗
An inbound rule in the database's security group that allows traffic from the web server's private IP address.
Why it's wrong here
Using private IP is not scalable; use security group reference.
✓
An inbound rule in the database's security group that references the web server's security group.
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.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: An inbound rule in the database's security group that references the web server's security group. — Option B is correct because a security group on the database must allow inbound traffic from the web server's security group. Option D is correct because the private subnet route table does not need a route to the internet gateway, but it must have a route to the NAT gateway or VPC peering if needed, but for database access, no route to internet is needed. However, the question asks for required components. Actually, to allow the web server to connect to the database, you need a security group rule on the database allowing the web server's security group, and you need the private subnet to have a route to the public subnet's CIDR via the local route (already present). So the correct options are B and C? Wait, let's analyze: A is not required because you can use security group IDs. B is required. C is required because the private subnet must have a route to the public subnet's CIDR (which is local and automatically added). D is not required because internet gateway is not needed for private subnet to communicate within VPC. E is not required because NAT gateway is for internet access. So the two correct are B and C. But C says "A route table associated with the private subnet that includes a route to the internet gateway" which is wrong. I need to correct the options. Let me rephrase:
What should I do if I get this ANS-C01 question wrong?
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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