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Question 587 of 1,546

Networking and Content Delivery →hardMultiple ChoiceObjective-mapped

SOA-C02 Networking and Content Delivery Practice Question

This SOA-C02 practice question tests your understanding of networking and content delivery. 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 a VPC with a CIDR of 10.0.0.0/16. They have two subnets: subnet-A (10.0.1.0/24) and subnet-B (10.0.2.0/24). An EC2 instance in subnet-A needs to send traffic to an EC2 instance in subnet-B. Both instances are in the same VPC and have appropriate security group rules. However, traffic is not reaching the destination. What is the MOST likely cause?

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 subnet-A does not have a route for subnet-B's CIDR.
Why wrong: The default local route in the VPC's main route table covers all subnets within the VPC CIDR.
B
The network ACL associated with subnet-B is denying inbound traffic from subnet-A.
Network ACLs are stateless; if the inbound rule does not allow traffic from subnet-A, it will be blocked.
C
The security group on the destination instance does not allow inbound traffic from the source instance.
Why wrong: The question states appropriate security group rules, so this is not the issue.
D
The VPC peering connection is not established between the two subnets.
Why wrong: Subnets within the same VPC do not need VPC peering; they communicate via the local route.

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 subnet-B is denying inbound traffic from subnet-A.

Option B is correct because network ACLs are stateless and must allow both inbound and outbound traffic for the communication to succeed. If the NACL associated with subnet-B does not allow inbound traffic from subnet-A (10.0.1.0/24), then traffic from the EC2 instance in subnet-A to the instance in subnet-B will be denied. Option A is incorrect because VPC route tables automatically include a local route for the VPC CIDR (10.0.0.0/16), so no specific route for subnet-B's CIDR is needed. Option C is incorrect because security groups are stateful; if the source instance's security group allows outbound traffic, the return traffic is automatically allowed, and the question states that security group rules are appropriate. Option D is incorrect because VPC peering is not required for communication within the same VPC; both subnets are in the same VPC, so local routing applies.

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 subnet-A does not have a route for subnet-B's CIDR.
Why it's wrong here
The default local route in the VPC's main route table covers all subnets within the VPC CIDR.
✓
The network ACL associated with subnet-B is denying inbound traffic from subnet-A.
Why this is correct
Network ACLs are stateless; if the inbound rule does not allow traffic from subnet-A, it will be blocked.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The security group on the destination instance does not allow inbound traffic from the source instance.
Why it's wrong here
The question states appropriate security group rules, so this is not the issue.
✗
The VPC peering connection is not established between the two subnets.
Why it's wrong here
Subnets within the same VPC do not need VPC peering; they communicate via the local route.

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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The network ACL associated with subnet-B is denying inbound traffic from subnet-A. — Option B is correct because network ACLs are stateless and must allow both inbound and outbound traffic for the communication to succeed. If the NACL associated with subnet-B does not allow inbound traffic from subnet-A (10.0.1.0/24), then traffic from the EC2 instance in subnet-A to the instance in subnet-B will be denied. Option A is incorrect because VPC route tables automatically include a local route for the VPC CIDR (10.0.0.0/16), so no specific route for subnet-B's CIDR is needed. Option C is incorrect because security groups are stateful; if the source instance's security group allows outbound traffic, the return traffic is automatically allowed, and the question states that security group rules are appropriate. Option D is incorrect because VPC peering is not required for communication within the same VPC; both subnets are in the same VPC, so local routing applies.

What should I do if I get this SOA-C02 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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