I have the following problem:
I'm running Ubuntu 18.04 on a Lenovo Thinkpad Carbon 5th gen. A Lenovo P27u display is connected via USB-C, also used as power supply. I can use a i-tec USB3 hub + ethernet adapter without problems, when I connect it directly to my laptop. It shows up as two USB devices:
Bus 002 Device 013: ID 0bda:8153 Realtek Semiconductor Corp. Bus 002 Device 012: ID 2109:0813 VIA Labs, Inc.
However, when I plug it into one of the USB ports of my Lenovo P27u display, which is connected via USB-C to the laptop, I only see the USB hub device (VIA Labs, Inc.) but not the Realtek 8153 device. Naturally, it also does not show up in ifconfig then.
In lack of other hardware, I can not directly test, if this is related specifically to the display or if this is a problem, when connecting such adapters after a hub in general.
I also tried to install the Realtek 8152 driver from their webpage, which did not change anything.
Any ideas how to tackle this problem? Does anybody have similar hardware to troubleshoot this issue?
Edit, to clarify the connections:
The display (Lenovo P27u) is conneccted via USB-C to the laptop (Lenovo Carbon X1 5th, 2017 model).
The display has an integrated USB3 hub with 3 USB3 connectors (blue). There is a forth one colored in yellow, where opinions seem to disagree, if this is for charging only, but I'm not talking about that one.
The USB to ethernet adapter is a USB3 hub with one upstream and three USB3 downstream ports + one ethernet port.
As already written in the initial version of the question: if I connect the USB to ETH adapter to the USB3 connection on the laptop directly, it works. If I connect it to one of the USB3 ports on the display, which is then connected to the laptop via USB-C, it only shows up as USB3 hub, but not as ethernet adapter.