PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. 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 uses Cloud NAT to allow instances without external IPs to access the internet. They have a managed instance group (MIG) in us-central1 with 10 instances, all using the same Cloud NAT configured with a single NAT IP address. They notice that some instances are unable to connect to a specific external API endpoint, while others can. The error on the failing instances is 'Cannot connect to host'. The NAT IP is not blacklisted by the API. The Cloud NAT gateway has default settings with a minimum port per VM of 64 and a maximum of 65536. What is the most likely cause?
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.
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
✓
Port exhaustion is occurring; increase the number of NAT IPs or increase the minimum ports per VM.
Cloud NAT uses source network address translation (SNAT) and maps internal IPs to the NAT IP using ports. By default, Cloud NAT allocates a range of ports per VM. If the instances are making many connections, they may exhaust the allocated ports. The symptom that only some instances fail suggests that the failing instances may have run out of ephemeral ports. Option D is correct: Increase the number of NAT IP addresses or increase the minimum ports per VM.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The instances are using different service accounts, and the NAT is not configured to allow all.
Why it's wrong here
Cloud NAT applies to all instances in the subnet, regardless of service account.
✗
The Cloud NAT's idle timeout is set too low, causing connections to be dropped.
Why it's wrong here
Idle timeout would affect long-lived connections, but the error is immediate.
✗
The external API endpoint has a rate limit that is being hit by the NAT IP.
Why it's wrong here
If it were a rate limit, all instances would fail, not just some.
✓
Port exhaustion is occurring; increase the number of NAT IPs or increase the minimum ports per VM.
Why this is correct
Port exhaustion affects VMs that make many outbound connections; increasing NATIPs provides more ports.
Clue confirmation
The clue words "most likely", "minimum / minimize" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNE NAT questions on configuration and troubleshooting.
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Port exhaustion is occurring; increase the number of NAT IPs or increase the minimum ports per VM. — Cloud NAT uses source network address translation (SNAT) and maps internal IPs to the NAT IP using ports. By default, Cloud NAT allocates a range of ports per VM. If the instances are making many connections, they may exhaust the allocated ports. The symptom that only some instances fail suggests that the failing instances may have run out of ephemeral ports. Option D is correct: Increase the number of NAT IP addresses or increase the minimum ports per VM.
What should I do if I get this PCNE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNE NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "minimum / minimize". 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?
Static NAT maps one inside address to one outside address.
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