The answer is to use a Cloud Router with BGP and establish multiple BGP sessions over each Interconnect. This is correct because BGP automatic failover across multiple interconnects relies on dynamic routing: when a BGP session detects a link failure, it withdraws the affected routes, and the Cloud Router instantly redistributes traffic across the remaining active sessions without any manual intervention. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how BGP’s route withdrawal mechanism provides built-in redundancy, often contrasting it with static routes or single-session setups that would require manual failover. A common trap is assuming that simply having multiple interconnects is enough—without multiple BGP sessions per interconnect, a single session failure could still blackhole traffic. Remember the memory tip: “One session per link is a single point of blink; multiple sessions keep the traffic in sync.”
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 multinational corporation is connecting five on-premises data centers to Google Cloud using Cloud Interconnect. Each data center has a dedicated 10 Gbps connection. They want to ensure that if one Interconnect fails, traffic is automatically redistributed across the remaining connections without manual intervention. Which solution meets this requirement?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a Cloud Router with BGP and establish multiple BGP sessions over each Interconnect
Option D is correct because Cloud Router with BGP enables dynamic routing, allowing multiple BGP sessions over each Cloud Interconnect. When one interconnect fails, BGP withdraws the affected routes, and traffic is automatically redistributed across the remaining BGP sessions without manual intervention. This meets the requirement for automatic failover and load balancing across the five 10 Gbps connections.
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.
✗
Configure multiple VLAN attachments on a single Cloud Router and rely on link aggregation
Why it's wrong here
Link aggregation does not provide failover across separate Interconnects.
✗
Deploy Cloud VPN tunnels as backup and configure static routes with lower priority
Why it's wrong here
Cloud VPN requires manual failover unless using BGP, but that adds complexity.
✗
Configure VPC Network Peering between all data centers and Google Cloud
Why it's wrong here
VPC Network Peering is for VPC-to-VPC, not on-premises.
✓
Use a Cloud Router with BGP and establish multiple BGP sessions over each Interconnect
Why this is correct
BGP with ECMP allows automatic failover across multiple Interconnects.
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 static routes or VPN tunnels can provide seamless automatic failover for high-bandwidth interconnects, but the correct approach requires dynamic BGP routing to react to link failures without manual intervention.
Detailed technical explanation
How to think about this question
Cloud Router uses BGP (Border Gateway Protocol, RFC 4271) to exchange routes with on-premises routers over each Cloud Interconnect VLAN attachment. When a BGP session goes down due to interconnect failure, the Cloud Router withdraws the corresponding prefixes from its routing table, and the remaining BGP sessions automatically advertise and install the routes, enabling sub-second failover. In a real-world scenario, you would configure each interconnect with a separate BGP session and use AS-path prepending or MED (Multi-Exit Discriminator) to influence traffic flow, ensuring optimal load distribution across the five 10 Gbps links.
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: Use a Cloud Router with BGP and establish multiple BGP sessions over each Interconnect — Option D is correct because Cloud Router with BGP enables dynamic routing, allowing multiple BGP sessions over each Cloud Interconnect. When one interconnect fails, BGP withdraws the affected routes, and traffic is automatically redistributed across the remaining BGP sessions without manual intervention. This meets the requirement for automatic failover and load balancing across the five 10 Gbps connections.
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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Question Discussion
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