MultipleNatFound means that you have two layers of network address translation going on which will prevent Roon ARC from working.
This could be caused locally on your own network if you have two devices acting as a router in which case you need to do one of:
Remove one of the routers from your network.
Reconfigure one of the devices to work as a ‘modem only’ (the router connected to the incomming internet connection) or a bridge/access point (a second router (for example some mesh WiFi systems).
However, it can also be seen if your Internet Service Provider uses CGNAT in order to re-use IPv4 addresses (which are in exceedingly short supply). In this case, you will need to contact your service provider to see whether they can offer a non-CGNATted solution.
Please see the above response; @Wade_Oram is correct and you’ll need to follow one of the aforementioned steps to remove the extra layer of Network Address Translation (NAT).
If you’re still having trouble after reconfiguring your setup, please follow up with the name of your ISP, as we might be able to point you in the right direction. Thank you!
I followed the instructions and contacted my service provider in order for him to cancel my NAT.
After cancelling , everything indeed worked perfectly -yesterday all day.
However,I shut down my Mac mini M1 at night and started it this morning to find out the the roon server ip has changed from 236 to 237 at the end of the ip address - while testing the connection I received the following message:-
If you have an explicit port forwarding rule on your router but your server has changed it’s ip address after rebooting, you will have to update the port forwarding rule to match.
To avoid this in the future your can, on your router, set up a ‘port reservation’ for your roon server (Mac Mini M1) such that it always gets assigned the same ip address by the routers DHCP. You will need to know your Mac Mini’s ethernet MAC address (6 hex digit pairs separated by colons - e.g. D8:3A:DD:9A:6E:03).