How to Configure Ubuntu to Access Internet only with Wifi Ignoring Wire Connection (Ethernet)

Context:

• the Wifi connection works perfectly with the DHCP of the router. Only with this connection, I can navigate the web.
• the wire connection is necessary for me to be connected directly with an embedded system. In the middle, there is a Switch and the only thing I do is to set up the address IP of both (laptop and embedded system). The systems speak perfectly using ssh etc. No problem here.
• OS Xubuntu 16.04 on my laptop and a Linaro on the embedded (please note: the problem is the same for 18.04 and the solution proposed in the answer works properly).

Problem: When I am connected to the system with the ethernet connection, it is impossible for me to navigate on the web. I guess it is because the laptop tries to access using the ethernet connection. Of course, the ethernet connection goes only to the embedded system (no web from this side).

Question: Can I use the ethernet only for the system and the wifi to continue to navigate the web pages? How can I do that?

Please note: I would like to use both (1) the wifi to navigate and (2) the ethernet for the embedded system AT THE SAME TIME. Separately they work perfectly

Solution 1:

I have a similar setup with an Ubuntu 18.04 LTS with both Ethernet and WiFi connection. The WiFi connects to the router and the Internet. The Ethernet cable connects to a Raspberry Pi.

For Ubuntu 16.04, this answer may be useful: Connecting PC and RaspberryPi using LAN cable

The instructions below are for Ubuntu 18.04

Go to System Setup menu > Network tab on the left margin > The cog icon for the Wired connection as shown below:

Go to the IPv4 tab of the Wired Connection and check the box Use this connection only for resources on its network as shown below.

That was all. I let the desktop assign the IP by DHCP and changed the Pi's setting to request a specific IP address from the desktop. It works for me.

If you manually assign IP addresses then do not specify any Gateway IP address in this setting. A Gateway is not needed in this setup and will confuse the kernel-level packet routing. Thanks Thomas Ward.

Hope this helps

Solution 2:

Thanks to @user68186 I have found the solution on Xubuntu 16.04:

Double click on the network connection (in my case the little symbol of wireless on top-right)

Choose > Edit connection... and select the connection you want to edit (in my case the Wire Connection 1):

From the window that will be open, select the tab IPv4:

Organize the network as you prefer (in my case no DHCP but a P2P connection with a little embedded system and a switch in the middle). Now press Routes on the bottom-right side and select the option Use this connection only for resource on this network:

Press Ok and Save the setup.

The wifi for internet and the ethernet for the P2P are working perfectly at the same time. Thanks @user68186