The answer is to increase the number of NAT IPs. This resolves Cloud NAT port exhaustion because a single NAT IP address provides a limited pool of source ports—roughly 64,000 per protocol—and each outbound TCP or UDP session consumes one unique port. When all ports are in use, new connections fail, which is exactly the symptom described. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of how Cloud NAT scales with concurrent connections; a common trap is to assume the fix involves adjusting firewall rules or switching to a different NAT type, but the core issue is the port pool size. Remember that adding more NAT IPs multiplies the available ports linearly, directly fixing connectivity without altering security policies. A simple memory tip: “One IP, one port pool; more IPs, more connections.”
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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.
A company is using Cloud NAT to allow instances in a private subnet to access the internet. They notice that some instances are unable to reach external services. The NAT gateway is configured with a single IP address. Which action would most likely resolve the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the number of NAT IPs
The issue is that a single NAT IP address can run out of available ports (each TCP/UDP session consumes a unique source port), causing new connections to fail. Increasing the number of NAT IPs expands the port pool, allowing more concurrent outbound connections. This directly addresses the port exhaustion problem without changing firewall rules or NAT type.
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.
✗
Change the NAT type to static
Why it's wrong here
Static NAT is for specific mappings, not for scaling outbound connections.
✗
Change the VPC firewall rules to allow egress from the NAT IP
Why it's wrong here
Firewall rules apply to the instance's internal IP, not the NAT IP. This is not necessary.
✓
Increase the number of NAT IPs
Why this is correct
More NATIPs increase available ports, reducing the chance of port exhaustion.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable TCP established connections only
Why it's wrong here
This is not a Cloud NAT feature. Cloud NAT automatically handles connections.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that firewall rules or NAT type changes fix connectivity issues, when the real problem is port exhaustion from a single NAT IP under heavy connection load.
Detailed technical explanation
How to think about this question
Cloud NAT uses source network address translation (SNAT) to map private IPs to a public IP. Each outbound connection consumes a source port from the NAT IP's port range (default 64,512 ports per IP). When all ports are in use, new connections are dropped (port exhaustion). Increasing the number of NAT IPs multiplies the available port pool linearly (e.g., 2 IPs = 129,024 ports). This is a common issue in high-throughput environments like web scraping or API calls from many instances.
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.
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the number of NAT IPs — The issue is that a single NAT IP address can run out of available ports (each TCP/UDP session consumes a unique source port), causing new connections to fail. Increasing the number of NAT IPs expands the port pool, allowing more concurrent outbound connections. This directly addresses the port exhaustion problem without changing firewall rules or NAT type.
What should I do if I get this PCSE 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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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