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Question 953 of 1,705

Network Management and Operations →hardMultiple 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 multiple subnets across Availability Zones. An application load balancer (ALB) is deployed in public subnets. The network team notices that traffic from the ALB to targets in private subnets is intermittently failing. The targets are healthy. 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 ALB is not associated with a public subnet.
Why wrong: The ALB is already associated with a public subnet. This is not the cause because the ALB is in public subnets and can reach private subnet targets.
B
The target security group does not allow traffic from the ALB's security group.
Correct. The target security group must allow inbound traffic from the ALB's security group. Without this rule, traffic from the ALB will be blocked.
C
The network ACL for the target subnets blocks outbound traffic.
Why wrong: The network ACL for the target subnets blocks outbound traffic: Incorrect. Network ACLs are stateless; if they blocked outbound traffic from targets, the targets would not be able to send responses, but the failure is on the inbound traffic from ALB to targets. Also, the question states targets are healthy, implying they can send responses. The issue is likely with the security group inbound rule.
D
Cross-zone load balancing is disabled.
Why wrong: Cross-zone load balancing is disabled: Incorrect. Cross-zone load balancing is enabled by default for ALBs and would not cause intermittent failures. It affects how traffic is distributed across zones, not whether traffic reaches targets.

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 target security group does not allow traffic from the ALB's security group.

The ALB communicates with targets using its private IP addresses. For traffic to reach the targets, the target security group must allow inbound traffic from the ALB's security group. If this rule is missing, traffic from the ALB will be dropped by the target security group, even though the targets are healthy. Option A is incorrect because the ALB is already deployed in public subnets, so it is associated with a public subnet. Option C is incorrect because network ACLs are stateless and only affect traffic crossing subnet boundaries; if the NACL blocked outbound traffic from targets, there would be issues with response traffic, but the question states traffic from ALB to targets is failing, so the issue is likely inbound to targets. Option D is incorrect because cross-zone load balancing is enabled by default and would not cause intermittent failures; it only affects distribution of traffic across zones.

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 ALB is not associated with a public subnet.
Why it's wrong here
The ALB is already associated with a public subnet. This is not the cause because the ALB is in public subnets and can reach private subnet targets.
✓
The target security group does not allow traffic from the ALB's security group.
Why this is correct
Correct. The target security group must allow inbound traffic from the ALB's security group. Without this rule, traffic from the ALB 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 network ACL for the target subnets blocks outbound traffic.
Why it's wrong here
The network ACL for the target subnets blocks outbound traffic: Incorrect. Network ACLs are stateless; if they blocked outbound traffic from targets, the targets would not be able to send responses, but the failure is on the inbound traffic from ALB to targets. Also, the question states targets are healthy, implying they can send responses. The issue is likely with the security group inbound rule.
✗
Cross-zone load balancing is disabled.
Why it's wrong here
Cross-zone load balancing is disabled: Incorrect. Cross-zone load balancing is enabled by default for ALBs and would not cause intermittent failures. It affects how traffic is distributed across zones, not whether traffic reaches targets.

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 target security group does not allow traffic from the ALB's security group. — The ALB communicates with targets using its private IP addresses. For traffic to reach the targets, the target security group must allow inbound traffic from the ALB's security group. If this rule is missing, traffic from the ALB will be dropped by the target security group, even though the targets are healthy. Option A is incorrect because the ALB is already deployed in public subnets, so it is associated with a public subnet. Option C is incorrect because network ACLs are stateless and only affect traffic crossing subnet boundaries; if the NACL blocked outbound traffic from targets, there would be issues with response traffic, but the question states traffic from ALB to targets is failing, so the issue is likely inbound to targets. Option D is incorrect because cross-zone load balancing is enabled by default and would not cause intermittent failures; it only affects distribution of traffic across zones.

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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