- A
The firewall rule allowing traffic on port 5432 is missing or misconfigured.
Why wrong: 'Connection refused' typically means the destination actively refused the connection, which can happen if the port is not open or the service is not running, rather than a firewall block.
- B
The instance is using an outdated SSL certificate.
Why wrong: SSL issues would result in different errors, such as SSL handshake failures or certificate errors, not 'Connection refused'.
- C
The database service is not running or is not listening on port 5432.
'Connection refused' indicates that the destination host is reachable but no service is listening on that port.
- D
The VPC network has no route to the database subnet.
Why wrong: If there were no route, the error would likely be 'Network is unreachable' or 'No route to host'.
Google PCA Ensure solution and operations reliability Practice Question
This PCA practice question tests your understanding of ensure solution and operations reliability. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Refer to the exhibit. An application running on a GCE instance (ID: 1234567890) is unable to connect to a database at 10.0.0.1:5432. The logs show repeated 'Connection refused' errors. 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.
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 database service is not running or is not listening on port 5432.
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.
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.
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 firewall rule allowing traffic on port 5432 is missing or misconfigured.
Why it's wrong here
'Connection refused' typically means the destination actively refused the connection, which can happen if the port is not open or the service is not running, rather than a firewall block.
- ✗
The instance is using an outdated SSL certificate.
Why it's wrong here
SSL issues would result in different errors, such as SSL handshake failures or certificate errors, not 'Connection refused'.
- ✓
The database service is not running or is not listening on port 5432.
Why this is correct
'Connection refused' indicates that the destination host is reachable but no service is listening on that port.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The VPC network has no route to the database subnet.
Why it's wrong here
If there were no route, the error would likely be 'Network is unreachable' or 'No route to host'.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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 PCA subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this PCA question test?
Ensure solution and operations reliability — This question tests Ensure solution and operations reliability — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The database service is not running or is not listening on port 5432.
What should I do if I get this PCA 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 PCA subnetting questions on CIDR, address ranges, and subnet selection.
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.
About these practice questions
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Last reviewed: Jul 4, 2026
This PCA practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCA exam.
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