Replicating VPC Peering Hub-and-Spoke with NCC Star Topology

PCNE By islever Editorial Last updated

Configuring Network Connectivity Center. Designing VPC networks.

Short answer

A Choose a Network Connectivity Center star topology, place the hub VPC in the center group and the spoke VPCs in the edge group to mirror non-transitive VPC peering.

Question

Your company deployed a hub and spoke architecture in Google Cloud to host their workloads. They use VPC network peerings to connect the hub and the spokes. You need to replicate the design and use Network Connectivity Center. What should you do?
  1. Choose a Network Connectivity Center star topology. Deploy the hub VPC in the center group. Deploy the spoke VPCs in the edge group. Correct Answer
  2. Choose a Network Connectivity Center star topology. Deploy the spoke VPCs in the center group. Deploy the hub VPC in the edge group.
  3. Choose a Network Connectivity Center mesh topology. Configure the hub and the spokes as Network Connectivity Center spokes.
  4. Choose a Network Connectivity Center mesh topology. Configure the spokes as Network Connectivity Center spokes.

Key Takeaways

It tests whether you know NCC's star topology replicates non-transitive VPC peering behaviour, and that the hub belongs in the center spoke group rather than the edge group.

This PCNE question tests replacing a VPC peering hub-and-spoke design with Network Connectivity Center. The correct choice is a star topology with the hub VPC in the center group and the spoke VPCs in the edge group (A), which preserves non-transitive spoke isolation.

Common mistake: Option C is the tempting trap: choosing a mesh topology because it looks like a hub-and-spoke drawing, but mesh is fully transitive and lets every spoke reach every other spoke, unlike VPC peering.

Expert Analysis

The decisive qualifier is "replicate the design." The existing design is VPC network peerings forming hub and spoke, and VPC peering is deliberately non-transitive: spoke-to-spoke traffic does not flow through the hub. So the NCC option you pick must reproduce that same, segmented behaviour, not improve on it.

Star versus mesh. NCC's star topology has two spoke groups — center and edge — with separate route tables. Routes from the center group propagate to the edge group and vice versa, but edge-to-edge routes are withheld. That is exactly the hub-and-spoke model, so star is correct and mesh (options C and D) is eliminated: mesh is fully transitive, every spoke learns every other spoke's routes, which would silently change the connectivity semantics you were asked to replicate.

Placement of the hub. In a star, the center group is the distribution point — it is the only group whose routes reach all other spokes. The hub VPC therefore belongs in the center group and the spoke VPCs in the edge group, which is option A. Option B inverts this: putting the spokes in the center group and the hub at the edge would leave the hub as just one peripheral spoke, giving no central distribution at all.

On the objection that "center group" and "edge group" are not VPC terms. Those spoke groups are NCC concepts that apply to all spoke types in a star topology, VPC spokes included; Google's VPC spokes overview describes exactly this arrangement. Option D additionally fails because it omits the hub VPC as a spoke, so there is no center at all. Answer: A.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

Read the constraint verb first — "replicate" means preserve existing behaviour, so ask what the current construct does (VPC peering = non-transitive) before evaluating options. Then eliminate any choice that adds connectivity: mesh always implies full transitivity. Finally check group placement against the direction of route propagation: the group that must distribute routes to everything else is the center group, and the central distribution point in the stated design is the hub.

Frequently Asked Questions

Why does Network Connectivity Center star topology replicate VPC peering hub-and-spoke?

In a star topology, center-group and edge-group spoke routes are kept in separate route tables, so edge spokes do not learn each other's routes. That reproduces VPC peering's non-transitive behaviour, where spokes only reach the hub.

Which NCC topology is transitive between spokes?

The mesh topology. Every spoke in a mesh learns routes from every other spoke, so spoke-to-spoke traffic flows directly. Choosing mesh would change a non-transitive VPC peering design into a fully connected one.

Where should the hub VPC go in an NCC star topology?

In the center spoke group, because only the center group's routes propagate to all edge spokes. The workload spoke VPCs go in the edge group; placing the hub at the edge (option B) removes the central distribution point.

More PCNE FAQ →

Community Votes

A
71%
C
29%

71% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 8 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 8

  1. b0b25 👍 3 Answered A
    Keeping Hub in Central and all spoke in edge group for NCC Star makes sense
  2. lolanczos 👍 2 Answered C
    This is C, guys. NCC doesn’t use terms like "center group" or "edge group" for VPCs. That terminology applies to partner interconnects using star topology for hybrid connectivity, not for interconnecting VPCs.
  3. Positron75 👍 1
    https://docs.cloud.google.com/network-connectivity/docs/network-connectivity-center/concepts/connectivity-topologies?hl=en#star-topology "The star topology has two spoke groups that provide network segmentation using separate route tables for each spoke group. The following route table rules apply to each spoke group: The center spoke group permits routes in its route table that let resources in spokes of the center group communicate with resources in spokes of either the center group or edge group. The edge spoke group only permits routes in its route table that let resources in spokes of the edge group communicate with resources in spokes of the center group. NCC prohibits routes in the edge spoke group route table that would provide connectivity among different spokes in the edge group."
  4. n2183712847 👍 1 Answered A
    To replicate the current VPC network peering hub-and-spoke design, you need the NCC topology that behaves similarly in terms of inter-spoke communication limitations. That is the Star topology. The "hub" VPC acts as the central point, and the "spoke" VPCs are the peripheral points.
  5. zzaric 👍 1 Answered A
    A 100% - you need to replicate VPC peering - no transitive. Mesh is transitive, and Star not. Who ever is in Center group can talk to each edge group.
Show 3 more comments
  1. Gwendal 👍 1 Answered A
    https://cloud.google.com/network-connectivity/docs/network-connectivity-center/concepts/vpc-spokes-overview#star-topology
  2. glb2 👍 1 Answered C
    C is correct.
  3. RKS_2021 👍 1 Answered A
    A is correct.

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