The Third Cloud Breaks Your Peering Model: Transitive Routing and the Hub Decision
Two clouds are easy to connect. A pair of private links, a handful of route tables, and traffic flows both ways. The design fits on a whiteboard and it works — until a third cloud arrives, usually through an acquisition, a GPU region that only exists on one provider, or a SaaS workload that had to live somewhere specific. That is the moment most multi-cloud networks quietly break. Not with an…
As a multi-cloud network expands beyond two clouds, connectivity becomes increasingly complex. Connecting a third cloud, often through acquisition or a specific workload, can break the existing network design. Peering between networks is not transitive, meaning a direct connection is required between all networks, leading to a full mesh design.
The number of connections needed grows rapidly with each new cloud added. Adding a hub-and-spoke design replaces the full mesh with a single transit point for each cloud network. While this simplifies the design, it introduces trade-offs in latency, blast radius, and cost. Cloud-native transit services offer quick adoption and native route propagation but limit the overall network.
Self-managed routing provides full control but requires operational effort and testing. Managed overlay fabrics provide consistency across clouds but trade some provider-specific visibility. The key to a successful hub design is clear routing policy and validation at the hub before advertisement to prevent policy failures.
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