The answer is to advertise the VPC’s IP range to the on-premises network. Cloud Router uses BGP to dynamically exchange routes over a VPN tunnel or Dedicated Interconnect, and in hybrid connectivity, its primary purpose is to announce the VPC’s subnet CIDR to the on-premises router, ensuring on-premises hosts can route return traffic back to the VPC. On the Google Professional Cloud Network Engineer exam, this concept tests your understanding of how BGP sessions enable route advertisement rather than static routing, often appearing in scenarios where you must distinguish between advertising VPC ranges versus on-premises ranges. A common trap is assuming Cloud Router’s BGP configuration is for receiving routes only, but the key is that it advertises the VPC’s IP range to establish bidirectional connectivity. Memory tip: think “Cloud Router shouts VPC IPs to on-prem” — it’s the advertiser, not just the listener.
PCNE Practice Question: Designing, planning, and prototyping a GCP network
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. 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.
Exhibit
Refer to the exhibit.
```
Resource: Cloud Router
Name: router-1
Region: us-central1
Network: vpc-1
BGP: Autonomous System Number (ASN): 65001
Advertised IP ranges: 10.0.0.0/16
BGP sessions:
- peer: on-prem-router
peer ASN: 65002
peer IP: 192.168.1.1
Cloud Router IP: 169.254.0.1
Advertised route priority: 100
Status: Established
On-premises router BGP table:
Network Next Hop Metric
10.0.0.0/16 169.254.0.1 0
0.0.0.0/0 192.168.1.1 0
```
Based on the exhibit, what is the purpose of Cloud Router's BGP configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To advertise the VPC's IP range to the on-premises network.
Cloud Router uses BGP to dynamically exchange routes between a VPC network and an on-premises network over a VPN tunnel or Dedicated Interconnect. In this configuration, the purpose is to advertise the VPC's IP range (the custom or auto-mode subnet CIDR) to the on-premises router, enabling on-premises hosts to route traffic back to the VPC. This is achieved by configuring the Cloud Router with a BGP session and setting the advertised route for the VPC's IP range.
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.
✓
To advertise the VPC's IP range to the on-premises network.
Why this is correct
Cloud Router advertises 10.0.0.0/16 to on-premises.
Related concept
Read the scenario before looking for a memorised answer.
✗
To load balance traffic across multiple VPN tunnels.
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that Cloud Router's primary function is to load balance traffic or receive default routes, but the core purpose is to dynamically advertise and learn specific IP prefixes via BGP for hybrid connectivity.
Trap categories for this question
Command / output trap
Only one BGP session is shown, no load balancing.
Detailed technical explanation
How to think about this question
Under the hood, Cloud Router implements BGP-4 (RFC 4271) and supports both eBGP and iBGP sessions. When advertising the VPC's IP range, Cloud Router uses the 'bgp' subcommand with 'advertised-ip-ranges' to specify the CIDR blocks, and the on-premises BGP peer must have a corresponding route import policy. A real-world scenario is hybrid cloud connectivity where the on-premises network needs to know the exact VPC subnets to route traffic without relying on a default route, ensuring precise traffic engineering and avoiding asymmetric routing.
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.
Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: To advertise the VPC's IP range to the on-premises network. — Cloud Router uses BGP to dynamically exchange routes between a VPC network and an on-premises network over a VPN tunnel or Dedicated Interconnect. In this configuration, the purpose is to advertise the VPC's IP range (the custom or auto-mode subnet CIDR) to the on-premises router, enabling on-premises hosts to route traffic back to the VPC. This is achieved by configuring the Cloud Router with a BGP session and setting the advertised route for the VPC's IP range.
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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