Can't get RTL8125B working on 20.04

So I did a fresh install of Ubuntu 20.04 on a computer with the new RTL8125B Realtek network card and I cannot get the network to work.

I was very suprised since this is supposed to be the new feature of the 5.4 kernel (I have 5.4.0-26-generic installed).

Does anyone have any idea on how to get it working? Thank you.

$ lspci -knn | grep Eth -A3
06:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller [10ec:8125] (rev 04)
Subsystem: ASUSTeK Computer Inc. RTL8125 2.5GbE Controller [1043:87d7]
Kernel modules: r8169
07:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 470/480/570/570X/580/580X/590] [1002:67df] (rev e7)

$ dmesg | grep -i r8169
[    0.911236] r8169 0000:06:00.0: unknown chip XID 641

I had the same exact issue. Looks like you're missing drivers for the Ethernet.

Go to this link (which is from the actual Ethernet provider): https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software

Download the "2.5G Ethernet LINUX driver r8125 for kernel up to 5.6" and follow the installation instructions.

You should be able to use wired connection once you're done.

The rtl8125b support has been added to the linux-next tree 6 days ago.

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/net/ethernet/realtek?h=next-20200720&id=0439297be95111cf9ef5ece2091af16d140ce2ef

It will take some time to get into stable and then into Ubuntu.

You can try to install drivers from the Realtek site before Linux supports it natively. You'll need to disable Secure Boot in BIOS and blacklist r8169 to get them working.

The issue is fixed in the 5.9 kernel. Unfortunately Ubuntu 20.10 and 20.04.2 won't have this kernel. So a mainline kernel, or a backport is needed.

There are no installation instructions on the realtek download page.

Anyways this solution worked for me:

Here's a solution I found;

    Go to the Realtek website 387

    Download the Unix(Linux) r8125 driver. You will need to give an email address.
    1754×445

    Go to /Downloads directory. Extract the Tarball.

    In Terminal, go into r8125-xxxx folder and run the autorun.sh

    $ sudo ./autorun.sh

Everything should run automatically and you should get ethernet connection now.

The problem happens with me on kernel 5.4 now with kernel 5.10 there is no problem.