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Question 674 of 1,705

Network Management and Operations →easyMultiple ChoiceObjective-mapped

ANS-C01 Network Management and Operations Practice Question

This ANS-C01 practice question tests your understanding of network management and operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 a VPC with a public subnet and a private subnet. The public subnet contains a web server (EC2 instance) that must be accessible from the internet. The private subnet contains a database server (EC2 instance) that should only be accessible from the web server. The web server's security group allows HTTP (80) and HTTPS (443) from 0.0.0.0/0. The database server's security group allows MySQL (3306) from the web server's security group. However, the web server cannot connect to the database server. The network engineer has verified that the web server can reach the internet and that the database server's security group is correctly configured. What is the most likely cause of the connectivity problem?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The route table for the private subnet does not have a route to the public subnet.
Why wrong: Incorrect: Route tables are not needed for traffic within the same VPC; subnets can communicate by default.
B
The web server's security group does not allow outbound traffic to the database server.
Why wrong: Incorrect: Security groups are stateful; outbound traffic is allowed if inbound is allowed.
C
The network ACL associated with the private subnet is blocking inbound MySQL traffic from the web server.
Correct: A custom NACL can block traffic even if security groups allow it.
D
The database server does not have a route to the internet gateway.
Why wrong: Incorrect: Internet gateway is not needed for internal VPC communication.

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

✓

The network ACL associated with the private subnet is blocking inbound MySQL traffic from the web server.

The correct answer is C. Security groups are stateful, meaning that if the web server initiates traffic to the database, the return traffic is automatically allowed regardless of outbound rules in the security group. However, network ACLs (NACLs) are stateless and require explicit inbound and outbound rules. In this scenario, the database server's security group is correctly configured to allow MySQL traffic from the web server's security group, indicating that the security group is not the issue. The most likely cause is that the network ACL associated with the private subnet is blocking inbound MySQL traffic (port 3306) from the web server. Option A is incorrect because the route table for the private subnet does not need a route to the public subnet for traffic within the same VPC; local routes handle that. Option B is incorrect because security groups are stateful, so outbound traffic from the web server to the database is allowed by default. Option D is incorrect because the database server does not need a route to the internet gateway for internal VPC communication.

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.

✗
The route table for the private subnet does not have a route to the public subnet.
Why it's wrong here
Incorrect: Route tables are not needed for traffic within the same VPC; subnets can communicate by default.
✗
The web server's security group does not allow outbound traffic to the database server.
Why it's wrong here
Incorrect: Security groups are stateful; outbound traffic is allowed if inbound is allowed.
✓
The network ACL associated with the private subnet is blocking inbound MySQL traffic from the web server.
Why this is correct
Correct: A custom NACL can block traffic even if security groups allow it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The database server does not have a route to the internet gateway.
Why it's wrong here
Incorrect: Internet gateway is not needed for internal VPC communication.

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.

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 Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The network ACL associated with the private subnet is blocking inbound MySQL traffic from the web server. — The correct answer is C. Security groups are stateful, meaning that if the web server initiates traffic to the database, the return traffic is automatically allowed regardless of outbound rules in the security group. However, network ACLs (NACLs) are stateless and require explicit inbound and outbound rules. In this scenario, the database server's security group is correctly configured to allow MySQL traffic from the web server's security group, indicating that the security group is not the issue. The most likely cause is that the network ACL associated with the private subnet is blocking inbound MySQL traffic (port 3306) from the web server. Option A is incorrect because the route table for the private subnet does not need a route to the public subnet for traffic within the same VPC; local routes handle that. Option B is incorrect because security groups are stateful, so outbound traffic from the web server to the database is allowed by default. Option D is incorrect because the database server does not need a route to the internet gateway for internal VPC communication.

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

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

CIDR notation defines the prefix length.

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