- A
The Cloud SQL instance's private IP address is not assigned to the correct subnetwork.
Why wrong: The ping test shows the IP is reachable, so it must be correctly assigned.
- B
The firewall rules need an explicit allow rule for TCP port 3306 for the server's IP range.
Why wrong: The default allow internal rule covers all protocols and ports, including TCP 3306.
- C
The Compute Engine server's service account does not have the Cloud SQL Client IAM role.
The Cloud SQL Client role is required to connect to Cloud SQL instances. The permission error aligns with missing IAM permissions.
- D
The Cloud SQL instance requires the public IP address to be enabled for the application to connect.
Why wrong: Private IP connectivity does not require a public IP. The ping test confirms private IP reachability.
Quick Answer
The answer is that the Compute Engine server’s service account lacks the Cloud SQL Client IAM role. While a successful ping confirms network-layer reachability via the VPC’s default allow internal rule, a permission error on the application connection points to an identity and access management issue, not a firewall or routing problem. Cloud SQL private IP connections still require the connecting principal—in this case, the VM’s service account—to be granted the Cloud SQL Client role, which authorizes client-level access to the instance. On the Google Professional Cloud Security Engineer exam, this scenario tests your ability to distinguish between network connectivity and IAM authorization, a common trap where candidates assume private IP bypasses IAM. Remember: private IP removes the public endpoint, but IAM still gates the connection. A useful memory tip is “ping is not permission”—network reachability does not equal database access.
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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 is using Cloud SQL with a private IP address in the same VPC as their Compute Engine web application server. The server can reach the Cloud SQL instance's IP address via ping, but the application is failing to connect with a permission error. The VPC firewall rules include the default allow internal rule. 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 Compute Engine server's service account does not have the Cloud SQL Client IAM role.
The default allow internal rule permits all protocols and ports, so network connectivity is fine. The permission error indicates insufficient IAM permissions. The Cloud SQL Client role is required for connecting to Cloud SQL instances via private IP.
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 Cloud SQL instance's private IP address is not assigned to the correct subnetwork.
Why it's wrong here
The ping test shows the IP is reachable, so it must be correctly assigned.
- ✗
The firewall rules need an explicit allow rule for TCP port 3306 for the server's IP range.
Why it's wrong here
The default allow internal rule covers all protocols and ports, including TCP 3306.
- ✓
The Compute Engine server's service account does not have the Cloud SQL Client IAM role.
Why this is correct
The Cloud SQL Client role is required to connect to Cloud SQL instances. The permission error aligns with missing IAM permissions.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The Cloud SQL instance requires the public IP address to be enabled for the application to connect.
Why it's wrong here
Private IP connectivity does not require a public IP. The ping test confirms private IP reachability.
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
The ping test shows the IP is reachable, so it must be correctly assigned.
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.
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 PCSE subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this PCSE question test?
Configuring network security — This question tests Configuring network security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Compute Engine server's service account does not have the Cloud SQL Client IAM role. — The default allow internal rule permits all protocols and ports, so network connectivity is fine. The permission error indicates insufficient IAM permissions. The Cloud SQL Client role is required for connecting to Cloud SQL instances via private IP.
What should I do if I get this PCSE 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 PCSE 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: Jun 24, 2026
This PCSE 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 PCSE exam.
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