The answer is that custom route exchange is not enabled on the VPC Network Peering connection. By default, VPC peering does not exchange custom routes, including subnet routes, unless explicitly configured, so VPC-B lacks a route to VPC-A’s 10.1.0.0/16 range, preventing traffic from reaching 10.1.0.2 even though the peering is active and firewalls allow ingress. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding that VPC peering route exchange is not automatic—a common trap is assuming an active peering status guarantees connectivity, but you must enable custom route export and import on both sides. Remember the memory tip: “Peering is just the handshake; routes are the map.”
PCSE Practice Question: Managing operations in a cloud solution environment
This PCSE practice question tests your understanding of managing operations in a cloud solution environment. 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 security engineer is troubleshooting a connectivity issue between two VPCs connected via VPC Network Peering. VPC-A (project A) has a Compute Engine instance with internal IP 10.1.0.2. VPC-B (project B) has an instance with internal IP 10.2.0.2. The engineer has verified that the peering connection is active and the firewall rules allow ingress from 10.1.0.0/16. However, the instance in VPC-B cannot ping the instance in VPC-A. 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 VPC-B does not have a route to VPC-A's subnet ranges. Custom route exchange is not enabled on the peering connection.
The most likely cause is that custom route exchange is not enabled on the VPC Network Peering connection. By default, VPC peering does not exchange custom routes (including subnet routes) unless explicitly enabled. Without this, VPC-B has no route to the 10.1.0.0/16 subnet of VPC-A, so the instance in VPC-B cannot send traffic to 10.1.0.2, even though firewall rules allow ingress. The peering connection being active only means the link is established, not that routes are automatically propagated.
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.
✗
The VPC-A has a firewall rule that denies ICMP traffic from VPC-B.
Why it's wrong here
The engineer verified firewall rules allow ingress from 10.1.0.0/16, so this is not the issue.
✓
The VPC-B does not have a route to VPC-A's subnet ranges. Custom route exchange is not enabled on the peering connection.
Why this is correct
By default, only subnet routes are exchanged. Custom routes require explicit export/import settings.
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.
✗
The MTU configuration on the peering connection is set too low.
Why it's wrong here
MTU issues would cause fragmentation, not complete unreachability.
✗
The instance in VPC-B does not have a public IP address.
Why it's wrong here
Ping uses internal IPs; public IPs are not required for VPC peering.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that an active peering connection and permissive firewall rules are sufficient for connectivity, when in fact route exchange (especially for custom routes) must be explicitly enabled for traffic to flow between VPCs.
Detailed technical explanation
How to think about this question
VPC Network Peering in Google Cloud relies on route exchange to enable connectivity between subnets. By default, only subnets that are directly peered (via the 'export custom routes' option) have their routes advertised to the peer. If custom route exchange is disabled, the peer VPC will not learn the subnet routes of the other VPC, resulting in no reachability even if firewall rules are permissive. This is distinct from AWS VPC Peering, where route tables must be manually updated; in GCP, the route exchange is automatic only for subnets when the peering is created, but custom routes (including those for subnets in different projects) require explicit export/import settings.
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
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Managing operations in a cloud solution environment — This question tests Managing operations in a cloud solution environment — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VPC-B does not have a route to VPC-A's subnet ranges. Custom route exchange is not enabled on the peering connection. — The most likely cause is that custom route exchange is not enabled on the VPC Network Peering connection. By default, VPC peering does not exchange custom routes (including subnet routes) unless explicitly enabled. Without this, VPC-B has no route to the 10.1.0.0/16 subnet of VPC-A, so the instance in VPC-B cannot send traffic to 10.1.0.2, even though firewall rules allow ingress. The peering connection being active only means the link is established, not that routes are automatically propagated.
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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