- A
Set a higher MED on the on-premises router for routes advertised to vlan-200, making vlan-100 preferred for all traffic.
Why wrong: This would send all traffic through vlan-100, not splitting per VPC.
- B
Configure static routes on the on-premises router to force traffic to VPC-A via vlan-100 and to VPC-B via vlan-200.
Why wrong: Static routes override BGP, but this could work, but it's not a best practice and does not leverage dynamic routing benefits.
- C
Create two separate VPCs and assign each VLAN attachment to a different VPC.
Why wrong: This is already the case; the problem is that on-premises routes are the same and both Cloud Routers see them.
- D
Use BGP community tags on the on-premises router to label routes for VPC-A and VPC-B, and configure route priority on Cloud Router to match these communities.
BGP communities allow granular route manipulation, ensuring traffic for each VPC uses the designated attachment.
Quick Answer
The answer is to use BGP community tags on the on-premises router to label routes for VPC-A and VPC-B, then configure route priority on Cloud Router to match these communities. This works because BGP community tags allow the on-premises router to attach specific metadata to route advertisements, enabling Cloud Router to distinguish between prefixes destined for different VPCs and apply local preference or MED values accordingly. By tagging routes for VPC-A with a community that Cloud Router 1 recognizes as higher priority, and tagging routes for VPC-B for Cloud Router 2, traffic is forced through the correct VLAN attachment, eliminating asymmetric routing. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how to solve asymmetric routing with Dedicated Interconnect without relying on static routes or blanket MED changes—a common trap is assuming MED alone works, but community tags provide granular per-VPC control. Memory tip: think of community tags as “colored labels” that tell each Cloud Router which VLAN is its designated lane.
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.
A company has a Dedicated Interconnect connection between their on-premises data center and Google Cloud. They have two VLAN attachments (vlan-100 and vlan-200) connected to two separate Cloud Routers in the same region. Each Cloud Router has a BGP session with the on-premises router. The on-premises router advertises the same prefixes (10.0.0.0/8) over both sessions. In Google Cloud, they have workloads in two different VPCs: VPC-A and VPC-B. They want traffic to VPC-A to use vlan-100, and traffic to VPC-B to use vlan-200. Cloud Router 1 is attached to VPC-A, Cloud Router 2 is attached to VPC-B. Currently, traffic from on-premises to VPC-A sometimes goes through vlan-200, causing asymmetric routing. What configuration change should they make to ensure traffic is symmetric?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use BGP community tags on the on-premises router to label routes for VPC-A and VPC-B, and configure route priority on Cloud Router to match these communities.
Option D is correct because BGP community tags allow the on-premises router to tag routes for VPC-A and VPC-B differently. Cloud Router can then use these community tags to influence route priority (e.g., via local preference or MED matching), ensuring that traffic to VPC-A is always routed through vlan-100 and traffic to VPC-B through vlan-200, solving the asymmetric routing issue without relying on static routes or MED manipulation that would affect all traffic.
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.
- ✗
Set a higher MED on the on-premises router for routes advertised to vlan-200, making vlan-100 preferred for all traffic.
Why it's wrong here
This would send all traffic through vlan-100, not splitting per VPC.
- ✗
Configure static routes on the on-premises router to force traffic to VPC-A via vlan-100 and to VPC-B via vlan-200.
Why it's wrong here
Static routes override BGP, but this could work, but it's not a best practice and does not leverage dynamic routing benefits.
- ✗
Create two separate VPCs and assign each VLAN attachment to a different VPC.
Why it's wrong here
This is already the case; the problem is that on-premises routes are the same and both Cloud Routers see them.
- ✓
Use BGP community tags on the on-premises router to label routes for VPC-A and VPC-B, and configure route priority on Cloud Router to match these communities.
Why this is correct
BGP communities allow granular route manipulation, ensuring traffic for each VPC uses the designated attachment.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume MED or static routes can solve asymmetric routing, but they overlook that MED affects all routes from a neighbor and static routes on-premises cannot control Google Cloud's return path selection, whereas BGP communities provide the necessary granularity to influence path selection per prefix in both directions.
Detailed technical explanation
How to think about this question
BGP community tags (RFC 1997) are a standard mechanism to tag routes with metadata; in Google Cloud, Cloud Router can be configured with custom route advertisements and can match on community tags to set local preference or MED, influencing best-path selection. This allows granular per-prefix path control without affecting other routes, unlike MED which is compared per-neighbor AS. In real-world scenarios, this is critical for traffic engineering in multi-homed environments where symmetric routing is required for stateful firewalls or NAT devices.
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.
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FAQ
Questions learners often ask
What does this PCNE question test?
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: Use BGP community tags on the on-premises router to label routes for VPC-A and VPC-B, and configure route priority on Cloud Router to match these communities. — Option D is correct because BGP community tags allow the on-premises router to tag routes for VPC-A and VPC-B differently. Cloud Router can then use these community tags to influence route priority (e.g., via local preference or MED matching), ensuring that traffic to VPC-A is always routed through vlan-100 and traffic to VPC-B through vlan-200, solving the asymmetric routing issue without relying on static routes or MED manipulation that would affect all traffic.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This PCNE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNE exam.
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