- A
Create a default VPC firewall rule that allows all egress traffic and assign only internal IPs to instances.
Why wrong: Without NAT, instances cannot reach the internet; they need a path through a NAT gateway or external IP.
- B
Configure Cloud NAT to provide outbound internet access for the instances and create a firewall rule that blocks inbound traffic from the internet.
Cloud NAT provides secure outbound-only internet access without exposing instance IPs.
- C
Use a managed instance group with a proxy instance that has an external IP, and route traffic through the proxy.
Why wrong: This adds complexity and a single point of failure; Cloud NAT is simpler and more scalable.
- D
Assign static external IP addresses to each instance and configure firewall rules to allow egress.
Why wrong: Assigning external IPs to instances is not secure; each instance becomes directly reachable from the internet.
Quick Answer
The answer is to configure Cloud NAT for private subnet internet access, as this provides the simplest and most secure method for outbound connectivity. Cloud NAT allows Compute Engine instances without external IPs to initiate outbound connections to the internet for updates, while a firewall rule blocking all inbound traffic from the internet prevents external attacks. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of minimizing attack surface by avoiding external IPs on instances, a common trap where candidates mistakenly assign public IPs for simplicity. The key distinction is that Cloud NAT handles outbound-only traffic, unlike a proxy instance which adds complexity and a single point of failure. Memory tip: think of NAT as a "one-way door" for updates—outbound allowed, inbound blocked.
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring 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.
You are configuring a new VPC network with a private subnet for Compute Engine instances that need to access the internet for updates. Which configuration is the simplest and most secure?
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
Configure Cloud NAT to provide outbound internet access for the instances and create a firewall rule that blocks inbound traffic from the internet.
Cloud NAT allows instances without external IPs to access the internet for outbound connections, while preventing inbound traffic. Option B is correct. Option A is incorrect because assigning external IPs to each instance increases attack surface and is less secure. Option C is incorrect because firewall rules allowing all egress are less secure than NAT. Option D is incorrect because redirecting through a proxy instance adds complexity and single point of failure.
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.
- ✗
Create a default VPC firewall rule that allows all egress traffic and assign only internal IPs to instances.
- ✓
Configure Cloud NAT to provide outbound internet access for the instances and create a firewall rule that blocks inbound traffic from the internet.
- ✗
Use a managed instance group with a proxy instance that has an external IP, and route traffic through the proxy.
Why it's wrong here
This adds complexity and a single point of failure; Cloud NAT is simpler and more scalable.
- ✗
Assign static external IP addresses to each instance and configure firewall rules to allow egress.
Why it's wrong here
Assigning external IPs to instances is not secure; each instance becomes directly reachable from the internet.
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.
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.
- →
Configuring network security — study guide chapter
Learn the concepts, then practise the questions
- →
Configuring network security practice questions
Targeted practice on this topic area only
- →
All PCSE questions
500 questions across all exam domains
- →
Google Professional Cloud Security Engineer study guide
Full concept coverage aligned to exam objectives
- →
PCSE practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related PCSE practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Configuring network security practice questions
Practise PCSE questions linked to Configuring network security.
Configuring access within a cloud solution environment practice questions
Practise PCSE questions linked to Configuring access within a cloud solution environment.
Ensuring data protection practice questions
Practise PCSE questions linked to Ensuring data protection.
Managing operations in a cloud solution environment practice questions
Practise PCSE questions linked to Managing operations in a cloud solution environment.
Supporting compliance requirements practice questions
Practise PCSE questions linked to Supporting compliance requirements.
PCSE fundamentals practice questions
Practise PCSE questions linked to PCSE fundamentals.
PCSE scenario practice questions
Practise PCSE questions linked to PCSE scenario.
PCSE troubleshooting practice questions
Practise PCSE questions linked to PCSE troubleshooting.
Practice this exam
Start a free PCSE practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: Configure Cloud NAT to provide outbound internet access for the instances and create a firewall rule that blocks inbound traffic from the internet. — Cloud NAT allows instances without external IPs to access the internet for outbound connections, while preventing inbound traffic. Option B is correct. Option A is incorrect because assigning external IPs to each instance increases attack surface and is less secure. Option C is incorrect because firewall rules allowing all egress are less secure than NAT. Option D is incorrect because redirecting through a proxy instance adds complexity and single point of failure.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More PCSE practice questions
- Match each IAM role to its typical use case.
- Match each encryption scope to its description.
- Match each CVE or security concept to its description.
- Match each Google Cloud logging/monitoring term to its definition.
- Drag and drop the steps to rotate a customer-managed encryption key (CMEK) in Cloud KMS in the correct order.
- Drag and drop the steps to configure a Cloud NAT for private VM instances in the correct order.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.