PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. 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.
A company uses Cloud NAT to enable outbound connectivity for private VMs. They notice that some VMs are not able to reach a specific external IP range. The VMs have no tags or service accounts. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VMs might be in a different subnet than the one where Cloud NAT is configured.
Option C is correct because Cloud NAT uses the source IP address of the VM to determine which NAT IP to use, and if the VM is not in the subnet where Cloud NAT is configured, it won't use that NAT. Option A is wrong because Cloud NAT does not require a default route via the NAT gateway; it works with dynamic routes. Option B is wrong because there is no static route requirement. Option D is wrong because Cloud NAT does use unique external IPs per VM if configured, but that wouldn't block traffic.
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.
✗
Cloud NAT requires each VM to have a unique external IP address.
Why it's wrong here
Cloud NAT can use shared IPs; unique IPs are optional.
✗
The VMs need a default route pointing to the NAT gateway.
Why it's wrong here
Cloud NAT does not require a default route via a gateway; it uses Private Google Access and routes.
✗
A static route must be created for the external IP range via the NAT gateway.
Why it's wrong here
Static routes are not needed for Cloud NAT; it automatically handles outbound traffic.
✓
The VMs might be in a different subnet than the one where Cloud NAT is configured.
Why this is correct
Cloud NAT is applied per subnet; VMs in other subnets won't use it unless also configured.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Configuring network services — This question tests Configuring network services — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The VMs might be in a different subnet than the one where Cloud NAT is configured. — Option C is correct because Cloud NAT uses the source IP address of the VM to determine which NAT IP to use, and if the VM is not in the subnet where Cloud NAT is configured, it won't use that NAT. Option A is wrong because Cloud NAT does not require a default route via the NAT gateway; it works with dynamic routes. Option B is wrong because there is no static route requirement. Option D is wrong because Cloud NAT does use unique external IPs per VM if configured, but that wouldn't block traffic.
What should I do if I get this PCNE 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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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