The answer is that the VPC connector's subnet does not have a route to the peered VPC where Cloud SQL resides. This is the most likely cause because Serverless VPC Access routes all outbound traffic from Cloud Run through the connector’s VPC, but peering does not automatically propagate routes—the connector’s subnet must have an explicit route pointing to the Cloud SQL private IP range in the peered VPC. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of transitive routing limitations: a VPC connector can only reach resources in its own VPC unless you manually add routes for peered networks. A common trap is assuming that VPC peering alone provides full connectivity, but the connector acts as a gateway and does not inherit peered routes. Remember the memory tip: “Peering is not transitive—if the connector can’t see it, you must route it.”
PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. 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.
You are using Serverless VPC Access to connect Cloud Run services to a VPC network. The connector is in us-central1 with a /28 subnet. You have a Cloud SQL instance (private IP) in the same region but in a different VPC network (peered). The Cloud Run service cannot reach the Cloud SQL instance. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VPC connector's subnet does not have a route to the peered VPC where Cloud SQL resides.
Option A is correct because Serverless VPC Access routes traffic through the connector's VPC, but if the Cloud SQL instance is in a different VPC (even peered), the connector does not automatically route to the peered VPC. You need to ensure the route for the Cloud SQL private IP range is present in the connector's VPC. Option B is wrong because Cloud SQL private IP is accessible within the same VPC. Option C is wrong because the Cloud SQL proxy is not required if direct access is configured. Option D is wrong because the connector does not use Private Google Access for Cloud SQL.
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 must have the Cloud SQL Proxy configured.
Why it's wrong here
Cloud SQL Proxy is for IAM authentication, not for connectivity.
✗
Serverless VPC Access requires Private Google Access to be enabled on the connector's subnet.
Why it's wrong here
Private Google Access is for Google APIs, not for Cloud SQL private IP.
✗
Cloud SQL requires an external IP for Serverless VPC Access connectivity.
Why it's wrong here
Cloud SQL can be accessed via private IP.
✓
The VPC connector's subnet does not have a route to the peered VPC where Cloud SQL resides.
Why this is correct
VPC peering does not automatically propagate routes; you must configure custom route exchange or create routes.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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.
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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Configuring network services — This question tests Configuring network services — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The VPC connector's subnet does not have a route to the peered VPC where Cloud SQL resides. — Option A is correct because Serverless VPC Access routes traffic through the connector's VPC, but if the Cloud SQL instance is in a different VPC (even peered), the connector does not automatically route to the peered VPC. You need to ensure the route for the Cloud SQL private IP range is present in the connector's VPC. Option B is wrong because Cloud SQL private IP is accessible within the same VPC. Option C is wrong because the Cloud SQL proxy is not required if direct access is configured. Option D is wrong because the connector does not use Private Google Access for Cloud SQL.
What should I do if I get this PCNE 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 PCNE 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.
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