The answer is that the on-premises router is filtering routes based on the BGP community or AS path. This is correct because Cloud Router BGP custom advertisement filtering allows you to attach specific BGP communities or manipulate AS-path attributes to the advertised prefixes, and the on-premises router can be configured to accept only routes matching certain community values or AS-path lengths. In this scenario, the VPC subnets (like 10.3.0.0/24) are likely tagged with a community or AS-path that the on-premises router rejects, while the two explicitly advertised ranges (10.1.0.0/24 and 10.2.0.0/24) lack that attribute, so they pass through. On the Google Professional Cloud Network Engineer exam, this tests your understanding that BGP filtering is a two-way street—Cloud Router custom advertisements are only half the story; the peer router’s inbound policy determines what is actually accepted. A common trap is assuming Cloud Router misconfiguration, but the key is that the on-premises router is the one dropping routes. Memory tip: “Custom ads send, but peers decide the end”—always check the receiver’s filter rules first.
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.
Refer to the exhibit. The Cloud Router is configured with custom BGP advertisements. The on-premises router receives only the two advertised ranges (10.1.0.0/24 and 10.2.0.0/24) but not the VPC subnets (e.g., 10.3.0.0/24). What is the most likely reason?
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 is filtering routes based on the BGP community or AS path.
Option D is correct because Cloud Router custom advertisements can include BGP communities or AS-path attributes that the on-premises router may be filtering. If the on-premises router is configured to reject routes based on these attributes (e.g., only accepting routes with a specific community or AS-path length), it would drop the VPC subnet routes even if they are advertised. The scenario states that only the two explicitly advertised ranges are received, indicating a filtering mechanism on the on-premises side rather than a Cloud Router misconfiguration.
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 on-premises router is configured to accept only prefixes longer than /24.
Why it's wrong here
The VPC subnet is /24 as well, so it should be accepted.
✗
The advertised route priority of 100 is too high, causing the routes to be ignored.
Why it's wrong here
Priority doesn't affect advertisement.
✗
The Cloud Router's custom advertisement includes both the ALL_SUBNETS group and the explicit ranges, so all subnets should be advertised.
Why it's wrong here
The configuration seems correct; the issue is likely on the on-premises side.
✓
The on-premises router is filtering routes based on the BGP community or AS path.
Why this is correct
On-premises routers often have ingress filters that can drop routes.
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 Cloud Router's custom advertisement configuration automatically overrides on-premises filtering, when in reality BGP attributes like communities and AS-path are the primary mechanisms for route filtering on the receiving side.
Detailed technical explanation
How to think about this question
BGP communities are transitive attributes that can be used to tag routes for filtering or policy actions (e.g., NO_EXPORT, NO_ADVERTISE). In Google Cloud, Cloud Router can attach custom communities to advertised routes, and on-premises routers often use route maps to match these communities or AS-path length to control route acceptance. A common real-world scenario is an on-premises router configured to reject routes with a specific community (e.g., 65000:100) or to only accept routes with an AS-path of a certain length, inadvertently dropping VPC subnet routes that carry different attributes.
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.
Configuring network services — This question tests Configuring network services — 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 is filtering routes based on the BGP community or AS path. — Option D is correct because Cloud Router custom advertisements can include BGP communities or AS-path attributes that the on-premises router may be filtering. If the on-premises router is configured to reject routes based on these attributes (e.g., only accepting routes with a specific community or AS-path length), it would drop the VPC subnet routes even if they are advertised. The scenario states that only the two explicitly advertised ranges are received, indicating a filtering mechanism on the on-premises side rather than a Cloud Router misconfiguration.
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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