- 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.
Configuring Cloud NAT for Private Subnet Internet Access
This PCSE practice question tests your understanding of pcse exam topics. 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?
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.
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 a default egress firewall rule that allows all outbound traffic is less secure than using Cloud NAT, which provides controlled outbound access. Option C is incorrect because using a proxy instance adds complexity and a single point of failure. Option D is incorrect because assigning static external IPs to each instance increases the attack surface and is less secure than using Cloud NAT.
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.
Visual reference
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.
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FAQ
Questions learners often ask
What does this PCSE question test?
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 a default egress firewall rule that allows all outbound traffic is less secure than using Cloud NAT, which provides controlled outbound access. Option C is incorrect because using a proxy instance adds complexity and a single point of failure. Option D is incorrect because assigning static external IPs to each instance increases the attack surface and is less secure than using Cloud NAT.
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.
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Last reviewed: Jun 24, 2026
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