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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
  • Please edit your question and add output of lspci -knn | grep Eth terminal command. – Pilot6 Jul 17 at 20:00
  • @Pilot6 I added the output. In the meantime I tried: realtek.com/en/component/zoo/category/… to no avail – Antonín Hoskovec Jul 19 at 22:18
  • I made a typo, please post the output of lspci -knn | grep Eth -A3 – Pilot6 Jul 19 at 22:20
  • done :) Thank you for the help. – Antonín Hoskovec Jul 19 at 22:27
  • Now please add output of dmesg | grep -i r8169 – Pilot6 Jul 19 at 22:31
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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.

| improve this answer | |
  • I did install the 5.8.0 kernel from mainline ubuntu but the card is still not working. – amarkovits Aug 6 at 8:45
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    It hasn't been added to 5.8. It should appear in 5.9. – Pilot6 Aug 6 at 8:50
  • I've installed realtek drivers and blacklisted the module, seems to work... for now. – Barnaba Aug 6 at 19:12
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    This is a way of running. It would be useful if you write an answer about which drivers you installed and how. – Pilot6 Aug 6 at 19:59
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    You understood this wrong. After a kernel upgrade the r8125 should be rebuilt against the new kernel. To avoid this you need to install it using dkms. – Pilot6 Sep 14 at 7:17
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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.

| improve this answer | |
  • I tried that (see the second comment under the main question), but until I had internet connection working on the computer, I couldn't install the necessary packages for the instalation/compilation... since the fresh install of Ubuntu does not come with even the build-essentials... – Antonín Hoskovec Aug 12 at 12:26
  • The above solution fixed my broken Ethernet LAN. Instructions are in the README file of the download from the link provided above by MrGoldWatch. I have a fresh install of ubuntu 20.04.1 on a new PC build with Gigabyte B550 Aorus Master with Realtek 8125B 2.5G Ethernet. Instructions are short and worked immediately, but I had to first install make using sudo apt-get install build-essential using a wifi connection. – Yosi Shibberu Aug 17 at 3:15
  • This worked for me on a Proxmox 6.2-1 distribution running on an ASRock Z490M-ITX/ac motherboard. Check the README file in the driver and run the autorun.sh script, then add the interface in /etc/network/interfaces. For me the new interface name was enp3s0. Linux proxmox 5.4.65-1-pve #1 SMP PVE 5.4.65-1 (Mon, 21 Sep 2020 15:40:22 +0200) x86_64 GNU/Linux – Dominic Clifton Oct 22 at 16:01

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