The answer is that the on-premises router does not support full line rate. Even with a 10 Gbps Dedicated Interconnect, a single VLAN attachment funnels all traffic through one physical interface on the customer router; if that router’s forwarding capacity is only 5 Gbps, it becomes the bottleneck regardless of the cloud side or lack of congestion. This scenario tests your understanding that Dedicated Interconnect throughput is not solely a function of the link speed—the on-premises hardware must be capable of processing packets at the full line rate. On the Google Professional Cloud Network Engineer exam, this is a common trap where candidates blame VLAN configuration or BGP settings, but the real culprit is often a router’s switching or routing performance limit. Remember the memory tip: “One VLAN, one pipe—if the router can’t keep up, the pipe stays half full.”
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 enterprise is using a 10 Gbps Dedicated Interconnect between their on-premises data center and Google Cloud. They measure throughput and find it is only 5 Gbps even though there is no congestion. The on-premises router is configured with a single VLAN attachment. 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 on-premises router does not support full line rate
A single VLAN attachment on a 10 Gbps Dedicated Interconnect means the on-premises router must handle all traffic through one physical interface. If the router lacks the forwarding capacity to process packets at 10 Gbps line rate, throughput will be capped at its maximum switching or routing performance, which in this case is 5 Gbps. This is a common hardware limitation, not a configuration or congestion issue.
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.
✗
BGP is not configured, causing routing loop
Why it's wrong here
BGP is needed for dynamic routing but not directly causing throughput limit.
✓
The on-premises router does not support full line rate
Why this is correct
The on-premises router may be the bottleneck.
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.
✗
MTU mismatch between on-premises and Google Cloud
Why it's wrong here
MTU would cause fragmentation, not half throughput.
✗
QoS policy is limiting throughput on Google Cloud side
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that throughput issues are always caused by configuration errors (e.g., MTU, BGP, QoS) rather than hardware limitations, leading candidates to overlook the router's actual forwarding capacity.
Detailed technical explanation
How to think about this question
Dedicated Interconnect uses VLAN attachments (VLANs 802.1Q) to map to a Cloud Router, and the on-premises router must support jumbo frames (MTU 1500 or 8896) and line-rate forwarding. Many enterprise routers, especially older models or those with software-based forwarding, have a maximum throughput per interface that is lower than the physical link speed due to CPU limitations or bus architecture. For example, a Cisco ISR 4451 with a 10 Gbps interface may only achieve 5 Gbps throughput under load because its forwarding engine is shared across multiple services.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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 on-premises router does not support full line rate — A single VLAN attachment on a 10 Gbps Dedicated Interconnect means the on-premises router must handle all traffic through one physical interface. If the router lacks the forwarding capacity to process packets at 10 Gbps line rate, throughput will be capped at its maximum switching or routing performance, which in this case is 5 Gbps. This is a common hardware limitation, not a configuration or congestion issue.
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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