We run a 9 site Meraki SD-WAN with dual MPLS and HA pairs of MXs at each site.
The way we have it set up is 8 edge sites where the MXs have their WAN ports connected to the MPLS provider's tail circuit/CE equipment. We then have a core site where the MPLSs terminate on routed switch ports. We then have the HA pair set up in concentrator mode plugged into the switches on a dedicated VLAN. The internet access for the core site is via a separate pair of firewalls, also connected to the same switches.
In the dashboard all sites have the same public IP for both WAN ports, this makes them route locally over the MPLS rather than trying to go over the internet.
Please feel free to ask more if that doesn't make sense, or you need more details.
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