Before deploying BGP, it is important to understand several key concepts.
All MXs can be configured in either NAT or VPN concentrator mode. There are important considerations for both modes. For more detailed information on concentrator modes, click here.
In this mode, the MX is configured with a single Ethernet connection to the upstream network. All traffic will be sent and received on this interface. This is the recommended configuration for MX appliances serving as VPN termination points into the datacenter.
There are several options available for the structure of the VPN deployment.
In a hub and spoke configuration, the MX security appliances at the branches and remote offices connect directly to specific MX appliances and will not form tunnels to other MX or Z-series devices in the organization. Communication between branch sites or remote offices is available through the configured VPN hubs. This is the recommended VPN topology for most deployments.
https://documentation.meraki.com/MX/Networks_and_Routing/BGP
Thank you alemabrahao and RaphaelL. What happens in the scenario when the first site is migrated to New HUB, but the other existing spoke sites are still pointing to the existing HUB. How does the traffic route between the spoke routed via new HUB and the rest of the spokes that are still pointing to the existing HUB.
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In case you just add the new hub to one spoke as primary hub
Spokenew - hub new - hub old -
Spoke old
And
Spoke old - hub old- spoke new