Connecting 2 Arduino (with Ethernet shields) with two Ethernet ports from one computer

This is a question not related strictly with Arduino. But I have search over the internet and I could't find an appropriate answer.

This is the thing:
I want to connect two Arduino from my mac mini (late 2014), using the built-in connection an a usb modem I have set up.
But it happens that it only works one at a time. Separately they work fine. But if I plug in a second cable the other connection fails.
Can you help me out with this?

more info:
I have configured the ip address as:
built-in ethernet:
arduino 1:
arduino 2:

The idea is to use Processing to send data via DMX to both Arduinos at the same time.

Maybe this is not the best way to do it, and you can help me out with a solution.
Thanks a lot.

Did you just make up that 2.0.0.x address or are you a person in France who was assigned that address my the owner? For local experiments you should use one of the three non-routing address ranges: "192.168.x.x" or "10.x.x.x", or "172.16.x.x through 172.31.x.x"

The problem may be that you are using the same address range (2.0.0 x) on both physical interfaces (ethernet and USB). I think it will work if you use the ethernet port and an ethernet switch or hub to connect the two Arduinos.

It may also work if you use separate address spaces on the two interfaces:
Ethernet: 192.168.1.x, Subnet mask:
USB Ethernet: 192.168.2.x, Subnet mask:

1 Like

Thank you! you saved me!
I config the second arduino and the USB with the addresses 10.0.0.x
and let the first connection (ethernet) with 2.0.0.x
and it works!

You shouldn't use that address since you might end up connecting to a server in France.

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