I am thinking to achieve something like that you'll need one of these solutions: An IPv6 connection. Each device can then get a public IPv6 address, and you can create an IPv6 firewall rule to allow all traffic in. This will only work for communication to other IPv6 devices. A block of public IP addresses from your ISP, and do a 1:1 NAT to each device. You could try asking Meraki support to enable "Layer 3 Inbound Firewall Rules", which substantially disables a lot of the security. Not as likely to work as the above two options. Basically it requires all security to be disabled, and to allow anything in from the Internet. It sounds like an incredibly bad idea to me.
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