The answer is to configure both ingress and egress rules in the perimeter. This is correct because VPC Service Controls enforces data boundaries by using ingress rules to define who can enter the perimeter and egress rules to specify which identities and services can leave it. To allow a specific service account in a peripheral project to access a managed service inside the protected perimeter, you must create an egress rule that explicitly permits that service account as the source identity and the managed service as the target, thereby enabling secure cross-perimeter access. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how egress rules govern outbound traffic from a perimeter, and a common trap is confusing ingress rules (which control inbound access) with egress rules. Remember the mnemonic: “Egress exits the perimeter; Ingress enters it.”
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An organization uses VPC Service Controls to protect Google Cloud APIs. They need to allow a specific service account in a peripheral project to access a managed service in a protected service perimeter. What should they configure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ingress and egress rules in the perimeter.
VPC Service Controls uses ingress and egress rules to control data exchange between a protected service perimeter and resources outside it. To allow a specific service account in a peripheral project to access a managed service inside the perimeter, you configure an egress rule on the perimeter that permits traffic from that service account to the protected service. This rule explicitly defines the allowed source identity (the service account) and the target service, enabling secure cross-perimeter access.
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.
✗
IAM conditions on the service account.
Why it's wrong here
IAM conditions are not used for VPC SC perimeters.
✗
Access levels in VPC Service Controls.
Why it's wrong here
Access levels apply to user identities, not service accounts.
✗
Private Google Access.
Why it's wrong here
Private Google Access is for on-premises access to Google APIs, not for VPC SC.
✓
Ingress and egress rules in the perimeter.
Why this is correct
Ingress/egress rules grant access to specific service accounts from outside the perimeter.
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 distinction between IAM conditions (which control permissions within a project) and VPC Service Controls rules (which control network-level access across perimeters), leading candidates to mistakenly choose IAM conditions when the question explicitly involves crossing a service perimeter boundary.
Detailed technical explanation
How to think about this question
Under the hood, VPC Service Controls enforces perimeter boundaries by intercepting API calls at the Google Front End (GFE) and checking the request's source identity and target service against ingress/egress rules. Egress rules support specifying a service account as the 'identity' field, allowing that principal to send requests to services outside the perimeter, while the perimeter's default deny still blocks all other traffic. In a real-world scenario, a data analytics project might need to write results to a BigQuery dataset in a protected perimeter; an egress rule with the analytics service account as the source identity enables this without exposing the entire perimeter.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ingress and egress rules in the perimeter. — VPC Service Controls uses ingress and egress rules to control data exchange between a protected service perimeter and resources outside it. To allow a specific service account in a peripheral project to access a managed service inside the perimeter, you configure an egress rule on the perimeter that permits traffic from that service account to the protected service. This rule explicitly defines the allowed source identity (the service account) and the target service, enabling secure cross-perimeter access.
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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