Networking – No Ethernet Connection Available in Ubuntu 20.04

Your netplan .yaml file is broken.

ls -al /etc/netplan # get .yaml filename

sudo lshw -C network # identify ethernet device name, enxxxxxx

Edit it with:

sudo pico /etc/netplan/*.yaml <-- change the * to your filename

Initially make its content the following, with EXACLY the same spacing, indentation, and no tabs:

network:
  version: 2
  renderer: networkd
  ethernets:
    en01:
      dhcp4: true
      dhcp6: true
      optional: true
  wifis:
    wlp6s0:
      dhcp4: true
      dhcp6: true
      access-points:
        "YourWifiNetworkName":
          password: "WifiNetworkPassword"

sudo netplan generate

sudo netplan apply

reboot

Update #1:

BIOS

You have BIOS version F1.

The current BIOS is version F2a, dated 6/16/2020, and can be downloaded here.

Note: Confirm that I have the correct web page for your motherboard model #.

Note: Have good backup before updating the BIOS.

kernel

With the newer ethernet controller that you have, you may need to run with a newer kernel than stock from Ubuntu 20.04.1.

Go here to download the latest 5.8.3 kernel. Get the 4 regular .deb files, not the lowlatency files.

Update #2:

Word is that not even kernel 5.8.3 supports the RTL8125! Kernel 5.9 is supposed to support it, but there is only a 5.9-rc2 (rc2 means release candidate #2) version available now... see https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.9-rc2/.

In the mean time, download this Linux driver from Realtek, and it should work. https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software. Get the one for "2.5G Ethernet LINUX driver r8125 for kernel up to 5.6"... and use your original 5.4.x kernel.

Update #3:

Ordered a $13 TP-Link USB 3.0 Ethernet dongle to be able to connect and download/install required Ubuntu packages. https://www.amazon.com/dp/B00YUU3KC6

Update #4:

Installed USB to Ethernet adapter. Installed build-essential. Built driver. Everything works. Wireless will be completed when the need arises. Will need to install wpasupplicant.

In my case the r8168 didn't work with the Gigabyte B550 Aorus Elite motherboard. So what I did was:

I also downloaded the driver from the realtek website at https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software but I had to connect my mobile phone via usb and share the internet connection with the desktop in order to download the 2.5G Ethernet LINUX driver r8125 for kernel up to 5.6

From a Terminal window run:

sudo apt install r8168-dkms (this package was needed in order to run the r8125-90004.01 diver script with no errors)

cd /home/username/Downloads

cd r8125-90004.01

sudo chmod +x autorun.sh

sudo ./autorun.sh

sudo reboot

Please keep in mind that, after a kernel update a re-install of the RTL8125 is nedeed. So it's a good ideia to keep the folder r8125-90004.01 in Downloads.