The answer is that subnet IP ranges in peered VPCs must not overlap. This is a fundamental constraint because VPC peering relies on exchanging routes between the two networks; if their CIDR blocks overlap, the routes become ambiguous, and Google Cloud cannot determine which VPC should receive traffic destined for a given IP address, causing the peering connection to fail or creating routing conflicts. On the Google Professional Cloud Network Engineer exam, this principle tests your understanding of how VPC peering differs from VPN or shared VPC, where overlapping ranges are sometimes tolerated. A common trap is assuming you can use overlapping ranges if you manually configure static routes, but peering requires non-overlapping subnets for dynamic route exchange to work. Remember the memory tip: “No overlap, no conflict—peering needs distinct IP districts.”
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.
Which TWO considerations are important when designing a VPC peering strategy between multiple projects in Google Cloud?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Subnet IP ranges in peered VPCs must not overlap
Option B is correct because VPC peering requires that subnet IP ranges in peered VPCs do not overlap. This is a fundamental constraint of VPC peering in Google Cloud: if two VPCs have overlapping CIDR blocks, routes cannot be exchanged unambiguously, and the peering connection will fail to establish or will cause routing conflicts. Overlapping ranges would break the ability to route traffic correctly between the VPCs, as there would be no way to determine which subnet a packet should be delivered to.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Peering is transitive by default
Why it's wrong here
Peering is not transitive unless route exchange is enabled.
✓
Subnet IP ranges in peered VPCs must not overlap
Why this is correct
Overlapping ranges cause routing issues.
Related concept
Read the scenario before looking for a memorised answer.
✗
Firewall rules in one VPC automatically apply to peered VPCs
VPC peering can only be used within the same project
Why it's wrong here
Cross-project peering is supported.
✓
Custom routes can be exchanged between peered VPCs if configured
Why this is correct
You can export custom routes.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that VPC peering is transitive by default, leading candidates to incorrectly select Option A, when in fact transitivity must be explicitly engineered.
Detailed technical explanation
How to think about this question
Under the hood, VPC peering in Google Cloud uses the underlying Google Cloud network fabric to create a direct, private connection between two VPCs. When custom routes are exchanged (Option E), each VPC learns the subnets of the other via dynamic route propagation, but the routes are not transitive — they are only shared between the two directly peered VPCs. A real-world scenario where this matters is when designing a hub-and-spoke topology: you cannot simply peer spoke VPCs to a hub and expect spoke-to-spoke communication without additional configuration (e.g., using a VPN or a third-party appliance).
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configuring network services — This question tests Configuring network services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Subnet IP ranges in peered VPCs must not overlap — Option B is correct because VPC peering requires that subnet IP ranges in peered VPCs do not overlap. This is a fundamental constraint of VPC peering in Google Cloud: if two VPCs have overlapping CIDR blocks, routes cannot be exchanged unambiguously, and the peering connection will fail to establish or will cause routing conflicts. Overlapping ranges would break the ability to route traffic correctly between the VPCs, as there would be no way to determine which subnet a packet should be delivered to.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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