The answer is two peering connections: one from VPC1 to VPC2, and one from VPC2 to VPC1. This is because VPC Network Peering in Google Cloud is unidirectional by design—a single peering connection only allows the initiating VPC to send traffic to the target VPC, not the reverse. For full bidirectional communication, each VPC must independently establish its own peering connection to the other, creating a symmetric pair. On the Google Professional Cloud Network Engineer exam, this concept tests your understanding that VPC peering is not automatically reciprocal; a common trap is assuming one connection suffices for two-way traffic. The exam often presents scenarios with non-overlapping subnets to distract from this directional requirement. Remember the memory tip: “One way out, one way back—two peering connections keep the traffic on track.”
PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 wants to connect two VPCs in the same project using VPC Network Peering. Each VPC has non-overlapping subnets. What is the minimum number of peering connections required to enable full bidirectional communication?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Two peering connections: one from VPC1 to VPC2, and one from VPC2 to VPC1.
VPC Network Peering requires a peering connection to be established in each direction to enable full bidirectional communication. A single peering connection from VPC1 to VPC2 only allows VPC1 to initiate traffic to VPC2; for VPC2 to initiate traffic back to VPC1, a separate peering connection from VPC2 to VPC1 is needed. Therefore, two peering connections (one from each VPC to the other) are the minimum required.
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.
✗
One peering connection from VPC1 to VPC2.
Why it's wrong here
One peering allows only one-way traffic unless both sides are set up.
✗
Two peering connections from each VPC to the other (total four).
Why it's wrong here
Two total is sufficient.
✓
Two peering connections: one from VPC1 to VPC2, and one from VPC2 to VPC1.
Why this is correct
VPC peering is unidirectional, so two connections are needed for full mesh.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
A Shared VPC with subnetworks from both VPCs.
Why it's wrong here
Shared VPC is for sharing subnets across projects, not for connecting distinct VPCs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a single peering connection is sufficient because they think of it as a bidirectional link, but VPC Network Peering in Google Cloud requires explicit peering in each direction for full bidirectional traffic flow.
Detailed technical explanation
How to think about this question
Under the hood, VPC Network Peering uses the Cloud Router's dynamic routing (BGP) to exchange routes, but each peering connection is a separate resource with its own route exchange configuration. Even with non-overlapping subnets, routes are only imported from the peer VPC when the peering connection is active in that direction; without a reciprocal peering, the remote VPC's routes are not present in the local VPC's routing table. In real-world scenarios, this is critical for services like load balancers or NAT gateways that need to initiate connections back to the originating VPC.
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: Two peering connections: one from VPC1 to VPC2, and one from VPC2 to VPC1. — VPC Network Peering requires a peering connection to be established in each direction to enable full bidirectional communication. A single peering connection from VPC1 to VPC2 only allows VPC1 to initiate traffic to VPC2; for VPC2 to initiate traffic back to VPC1, a separate peering connection from VPC2 to VPC1 is needed. Therefore, two peering connections (one from each VPC to the other) are the minimum required.
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.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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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