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Question 672 of 1,733

Operations and Maintenance →hardMultiple SelectObjective-mapped

NLB Health Check Configuration — Troubleshooting Steps

This PAS-C01 practice question tests your understanding of operations and maintenance. 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 runs SAP NetWeaver on AWS and uses a Network Load Balancer (NLB) to distribute traffic to multiple application servers. The operations team notices that the NLB is not properly routing traffic to healthy targets. Which three steps should the team take to diagnose the issue? (Choose THREE.)

A
Confirm that the target instances are registered in the target group and are in the Available state.
Unregistered or stopped instances will not receive traffic.
B
Check the security group rules on the target instances to ensure they allow traffic from the NLB's subnet.
Security groups must allow health check traffic.
C
Verify that the health check settings on the NLB target group are correct (e.g., ping path, port, protocol).
Incorrect health check settings can cause false unhealthy status.
D
Enable cross-zone load balancing on the NLB.
Why wrong: Cross-zone load balancing does not fix health check issues.
E
Review the CloudWatch metrics for the NLB to see if there are any anomalies.
Why wrong: CloudWatch metrics show symptoms but not root cause.

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

✓

Confirm that the target instances are registered in the target group and are in the Available state.

Option A is correct: Target instances must be registered in the target group and in the Available state for traffic to be routed to them. Option B is correct: Security group rules on target instances must allow traffic from the NLB's subnet for health checks and client traffic. Option C is correct: Health check settings (ping path, port, protocol) must be correctly configured so the NLB can determine target health. Option D is wrong: Cross-zone load balancing distributes traffic across all enabled Availability Zones but does not fix routing to healthy targets. Option E is wrong: CloudWatch metrics can show anomalies but are not a primary diagnostic step for routing to healthy targets; they are more useful for monitoring after initial configuration.

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.

✓
Confirm that the target instances are registered in the target group and are in the Available state.
Why this is correct
Unregistered or stopped instances will not receive traffic.
Related concept
CIDR notation defines the prefix length.
✓
Check the security group rules on the target instances to ensure they allow traffic from the NLB's subnet.
Why this is correct
Security groups must allow health check traffic.
Related concept
CIDR notation defines the prefix length.
✓
Verify that the health check settings on the NLB target group are correct (e.g., ping path, port, protocol).
Why this is correct
Incorrect health check settings can cause false unhealthy status.
Related concept
CIDR notation defines the prefix length.
✗
Enable cross-zone load balancing on the NLB.
Why it's wrong here
Cross-zone load balancing does not fix health check issues.
✗
Review the CloudWatch metrics for the NLB to see if there are any anomalies.
Why it's wrong here
CloudWatch metrics show symptoms but not root cause.

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.

Trap categories for this question

Command / output trap
CloudWatch metrics show symptoms but not root cause.

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

An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.

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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this PAS-C01 question test?

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

What is the correct answer to this question?

The correct answer is: Confirm that the target instances are registered in the target group and are in the Available state. — Option A is correct: Target instances must be registered in the target group and in the Available state for traffic to be routed to them. Option B is correct: Security group rules on target instances must allow traffic from the NLB's subnet for health checks and client traffic. Option C is correct: Health check settings (ping path, port, protocol) must be correctly configured so the NLB can determine target health. Option D is wrong: Cross-zone load balancing distributes traffic across all enabled Availability Zones but does not fix routing to healthy targets. Option E is wrong: CloudWatch metrics can show anomalies but are not a primary diagnostic step for routing to healthy targets; they are more useful for monitoring after initial configuration.

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

What is the key concept behind this question?

CIDR notation defines the prefix length.

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Same concept, more angles

1 more ways this is tested on PAS-C01

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company runs SAP on AWS and uses a Network Load Balancer (NLB) to distribute traffic to multiple EC2 instances. The Operations team needs to ensure that the NLB only sends traffic to instances that are healthy. Which health check configuration is appropriate for TCP traffic?

medium

A.ICMP ping
✓ B.TCP health check on the application port
C.HTTP health check on port 80
D.HTTPS health check on port 443

Why B: The correct health check for a Network Load Balancer (NLB) handling TCP traffic is a TCP health check on the application port (Option B). NLB supports TCP, HTTP, HTTPS, and TLS health checks, but for raw TCP traffic, a TCP health check directly verifies that the target port is open and responding, which is efficient and appropriate. Option A (ICMP ping) is incorrect because NLB does not support ICMP health checks. Options C and D (HTTP/HTTPS on ports 80/443) are unnecessary for TCP traffic and require the target to run an HTTP server, which may not be the case for all TCP applications.

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