Every time I boot Kubuntu picks the wrong network controller by default

[theyoyomaster]

I am trying to learn how to configure my system to specify which network adapter to use by default. I have a somewhat specific scenario, I have a Prism USB router that I use for VR gaming (it's a specific product that creates a discrete link between my windows desktop and my Quest 3 so that I get better performance when not tethered). It isn't supported in Linux so when I boot my PC into Kubuntu it is non-functional. Well, every single time I boot it decides that is the primary hard wired network connection and I have to manually select the real ethernet adapter on my motherboard that is plugged into my actual network.

I tried googling for network priorities and found a way to set it, but it never seems to work for my specific scenario. No matter what I do, Kubuntu wants to use the USB adapter over my integrated ethernet on my motherboard. Anyone have any thoughts?

[oshunluvr]

Please post the contents of /etc/netplan/01-network-manager-all.yaml (or similarly named file).

You can turn off a device with a netplan entry like:

network:
version: 2
ethernets:
interface:
activation-mode: off

[oshunluvr]

And state what version of Kubuntu you are using...

[oshunluvr]

I guess I assumed you have disabled the device in System Settings > Wifi & Internet then unchecked "Connect automatically..."

[theyoyomaster]

Please post the contents of /etc/netplan/01-network-manager-all.yaml (or similarly named file).

You can turn off a device with a netplan entry like:

network:
version: 2
ethernets:
interface:
activation-mode: off

All that's in that file is:

network:
version: 2
renderer: NetworkManager


I am on 25.04.

The device isn't listed discretely in system settings. It treats both as "Wired" and I am yet to find a way to manage them separately.

[oshunluvr]

What's the output of ip link

[theyoyomaster]

What's the output of ip link

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp14s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen
1000
link/ether 10:ff:e0:87:ff:9a brd ff:ff:ff:ff:ff:ff
altname enx10ffe087ff9a
3: enxc8a3629c9a41: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group defa
ult qlen 1000
link/ether c8:a3:62:9c:9a:41 brd ff:ff:ff:ff:ff:ff
4: wlp13s0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether e8:47:3a:e7:95:a0 brd ff:ff:ff:ff:ff:ff
altname wlxe8473ae795a0




enp14s0 is the correct one, enxc8a3629c9a41 is the VR USB hub.

[oshunluvr]

Try editing the yaml file an add this below "renderer: NetworkManager"

ethernets:
   enxc8a3629c9a41:
      activation-mode: off​

Restart networking or log out or reboot.

[theyoyomaster]

Still defaulted to the USB hub but now there is an additional copy of it available.

[oshunluvr]

Ok, weird. Seems netplan takes over after UDEV has defined the device. Probably going to require a custom UDEV entry for it.

[theyoyomaster]

So for someone fairly new to Linux, what exactly does that mean and how would I go about learning how to do that?

[oshunluvr]

So for someone fairly new to Linux, what exactly does that mean and how would I go about learning how to do that?

UDEV detects removable devices automatically and has "rules" as to what to do with them. I'm totally unfamiliar with your USB network device, and writing UDEV rules isn't really easy.

So it appears that what's happening is:

• UDEV finds the USB network device and "attaches" it as an ethernet device
• Netplan scans the network devices and for some reason picks the wrong one every time

It would probably be easier to use netplan to control both devices. I don't know why the above didn't work.

Before we get into that, you said System Settings shows both devices as one?

It's occurs to me that simply blocking the USB driver responsible for the device could solve this. Do do that:

First, edit the yaml file back to it's previous state.
Then find the driver name of the USB device - the output of "lsmod" should help with that.
Then add it to the blacklist using Konsole or other terminal:

sudo -i
modprobe -r <drivername>
echo "blacklist <drivername>" >> /etc/modprobe.d/blacklist.conf

Then update initramfs and reboot.

update-initramfs -c -k $(uname -r)
reboot