A very important observation, the
OSPF only works if you use a single LAN, that is, if you use VLAN on the MX you will not be able to enable OSPF.
Another quick thing is that the MX only announces its routes, so to know the networks of another device that is part of the OSPF area you will have to create statistical routes in the MX.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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