Your Meraki MS120 switch doesn't need to have any IP parameters configured for your WAN circuit. You just need to configure a L2 transit VLAN (any unused VLAN-ID) on the interfaces facing the WAN-router and the MX WAN-interfaces.
... View more
My recommendation - only plug an MS into a single MX. Remove those two redundant cables. It will be rock solid reliable then. IMHO, adding the extra cables, although intuitively increases redundancy, actually causes more failures.
... View more
