Route exchange with site-to-site data transfer

Network Connectivity Center provides full mesh connectivity between each spoke that has the data transfer feature enabled. If all spokes have the feature enabled, Network Connectivity Center propagates all routes that one spoke learns to all other spokes.

Network Connectivity Center topology.
Network Connectivity Center topology (click to enlarge)

In the preceding topology, Spokes A, B, and C are attached to the same hub and use Cloud Router to advertise prefixes into the hub.

To enable cross-region site-to-site traffic through hubs and spokes, you must enable global routing in the VPC network associated with the hub and spokes. If all spokes are located in the same region, then global routing isn't necessary because site-to-site traffic works without enabling global routing.

The following table shows how the hub propagates prefix advertisements to other spokes.

Routes from Spoke A Routes from Spoke B Routes from Spoke C
Routes exported to Spoke A 10.3.0.0/16 is reachable through Spoke B. 10.4.0.0/16 is reachable through Spoke C.
Routes exported to Spoke B 10.2.0.0/16 is reachable through Spoke A. 10.4.0.0/16 is reachable through Spoke C.
Routes exported to Spoke C 10.2.0.0/16 is reachable through Spoke A. 10.3.0.0/16 is reachable through Spoke B.

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