Two ethernet ports, same IP as device connected to other ethernet port

I have a small Device with two ethernet ports (NICs) running Ubuntu 16.04. The first ethernetport has a static IP address (for example 10.0.0.2) The second ethernetport has static IP address (for example 10.0.0.3) but is connected to a printer with the same IP address as the first ethernetport of my device (it has IP 10.0.0.2 in our example). As expected, the printer cannot communicate because there is a duplicate IP address on the network. My Linux Device does not know whether to send information to its own NIC or two the printer.

My question is: Can I control the network communication based on the devicename? Or is there any other way to solve this without having to change the IP addresses of Port 1 or the Printer?

3

1 Answer

No. You will have to move the printer on the network if you don't want to make it unnecessarily complicated for yourself.

To do what you want - correctly put your 'small device' between the printer and the network - you should connect to the main network on NIC 1, and connect NIC 2 to the printer alone. The printer and NIC 2 should be on another IP range so that devices on the main network cannot connect directly to the printer. For example, with the printer connected only to NIC 2:

• NIC 1: 10.0.0.3

• NIC 2: 192.168.1.100

• Printer: 192.168.1.101 (mask /24, gateway NIC 2's IP)

From there, you can have a program listen on NIC 1, modify the print job, then send it to the printer over NIC 2. Having NIC 2 on a different subnet has the added convenience of making the system automatically choose NIC 2 to connect to the printer.

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