PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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.
An organization has established a Dedicated Interconnect to Google Cloud. They can ping instances in a VPC subnet but cannot connect to a service running on a different subnet within the same VPC. 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 BGP routes for that subnet are not advertised.
The Dedicated Interconnect is up and the organization can ping instances in one subnet, which confirms that Layer 2 and basic Layer 3 connectivity (via the VLAN attachment) are working. However, the inability to reach a service on a different subnet within the same VPC indicates that the on-premises router does not have a route to that specific subnet. This is most likely because the BGP session is not advertising the prefix for that subnet, or the on-premises router is not receiving the route via BGP. Without the route, traffic from on-premises to that subnet will be dropped.
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 MTU is too small.
Why it's wrong here
MTU issues typically cause packet loss or drops, not selective connectivity.
✗
The firewall rules are blocking the traffic.
Why it's wrong here
Firewall rules apply to all traffic regardless of the interconnect, so ping would also be blocked.
✗
The VLAN attachment is down.
Why it's wrong here
If the VLAN attachment were down, no traffic would flow at all.
✓
The BGP routes for that subnet are not advertised.
Why this is correct
If the on-premises router does not advertise the subnet via BGP, the VPC will not know how to route traffic back.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that firewall rules are the default cause of connectivity issues within a VPC, but here the key clue is that ping to one subnet works, isolating the problem to route advertisement rather than security policies.
Detailed technical explanation
How to think about this question
When using Dedicated Interconnect, Google Cloud advertises VPC subnet routes to the on-premises router via BGP (eBGP). If the on-premises router does not receive a specific subnet prefix, it will not have a path to that subnet, and traffic will be dropped at the on-premises side. This can happen if the subnet is not included in the BGP route advertisement (e.g., due to a custom route advertisement filter or a missing VPC subnet route in Cloud Router). The ping to the first subnet works because that subnet's prefix is advertised, while the second subnet's prefix is missing from the BGP updates.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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.
Implementing hybrid interconnectivity — This question tests Implementing hybrid interconnectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The BGP routes for that subnet are not advertised. — The Dedicated Interconnect is up and the organization can ping instances in one subnet, which confirms that Layer 2 and basic Layer 3 connectivity (via the VLAN attachment) are working. However, the inability to reach a service on a different subnet within the same VPC indicates that the on-premises router does not have a route to that specific subnet. This is most likely because the BGP session is not advertising the prefix for that subnet, or the on-premises router is not receiving the route via BGP. Without the route, traffic from on-premises to that subnet will be dropped.
What should I do if I get this PCNE 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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