How to Advertise Spoke Subnets via Hub Cloud Router?

PCNE By islever Editorial Last updated

Short answer

B Create custom routes at the Cloud Router in the hub to advertise the subnets of the VPC spokes.

Question

Your organization has a hub and spoke architecture with VPC Network Peering, and hybrid connectivity is centralized at the hub. The Cloud Router in the hub VPC is advertising subnet routes, but the on-premises router does not appear to be receiving any subnet routes from the VPC spokes. You need to resolve this issue. What should you do?
  1. Create custom routes at the Cloud Router in the spokes to advertise the subnets of the VPC spokes.
  2. Create custom routes at the Cloud Router in the hub to advertise the subnets of the VPC spokes. Correct Answer
  3. Create a BGP route policy at the Cloud Router, and ensure the subnets of the VPC spokes are being announced towards the on-premises environment.
  4. Create custom learned routes at the Cloud Router in the hub to advertise the subnets of the VPC spokes.

Key Takeaways

Examined topic: Cloud Router route advertisement behavior in hub-and-spoke architectures; common trap: assuming automatic propagation or using BGP policies instead of static custom routes.

This question tests proper Cloud Router configuration for advertising VPC subnet routes across a hub-and-spoke topology. The community consensus confirms that manually creating custom routes at the hub Cloud Router is required to propagate spoke subnets to on-premises networks.

Common mistake: Option C is frequently chosen because candidates assume dynamic BGP route policies can override default routing behavior, but Cloud Routers do not automatically redistribute peer VPC routes into BGP without explicit custom route definitions.

Expert Analysis

Why the Answer Is Correct

In a hub-and-spoke VPC peering setup, Cloud Routers do not automatically advertise subnet routes from peer VPCs over BGP. To enable hybrid connectivity, you must explicitly define custom routes at the hub Cloud Router that match the spoke subnet ranges and set their next-hop appropriately. Once these custom routes are created, the hub Cloud Router will advertise them to your on-premises routers via BGP, resolving the missing route issue.

Why the Other Options Are Wrong

Option A fails because custom routes defined in spoke Cloud Routers only affect traffic originating from those spokes and cannot be advertised through the hub to external peers. Option C is incorrect because Cloud Routers lack traditional BGP route-map capabilities for redistributing peer routes; they rely on static custom route configurations instead. Option D is invalid since "custom learned routes" is not a supported feature in Google Cloud networking, making it a distractor.

Community Comment Notes

Several users initially debated between options B and C, highlighting the confusion around BGP policy versus static route advertisement. One comment correctly points out that the official documentation validates creating custom routes at the hub to handle this scenario. Another user notes that while BGP policies sound plausible, GCP's Cloud Router architecture strictly requires manual custom route entries for inter-VPC subnet propagation in hybrid setups.

Official Reference

https://cloud.google.com/network-connectivity/docs/router/how-to/advertising-custom-ip

This link opens the official vendor documentation in a new tab.

Exam Strategy

Always verify whether a service automatically propagates routes before assuming dynamic protocols like BGP will handle redistribution. For GCP Cloud Router questions involving hub-and-spoke topologies, remember that explicit custom route creation at the hub is almost always required for cross-VPC advertisement.

Community Votes

B
100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 3 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 3

  1. Gwendal 👍 1 Answered B
    https://cloud.google.com/network-connectivity/docs/router/how-to/advertising-custom-ip
  2. 7103685 👍 1 Answered B
    The answered checked is wrong, C
  3. 7103685 👍 1 Answered B
    Correct answer is B

Reader comments & corrections

No reader corrections yet — spotted an error or have a note? Share it below.

Log in to comment, report an error, or add a note about this question.

Submitted for moderation before publishing. Keep it helpful and respectful.

How to Resolve BGP Session Failures on Cloud Interconnect?

S-grade

Deploying Packet Mirroring Policies in GCP Regions

S-grade

Troubleshooting Asymmetric Traffic on Google Cloud Interconnect

S-grade

How to Configure DNS Forwarding Across Isolated VPC Networks?

S-grade

Practice All PCNE Questions

Access 80 questions with complete answers and detailed explanations.

View Full PCNE Practice Test →

← Back to PCNE Study Guide