TrueNAS Scale and RTL8125 rev 0c

TrueNAS General
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22

Thanks for the hint.

Unfortunately I only have a production system, thus I don’t want to try the Beta. However I try all new general updates.

23

Drivers are part of the Linux kernel (*). TrueNAS gets support for new hardware when its kernel changes. TrueNAS seems to like LTS kernels: TrueNAS 26 uses Debian Trixie as a base image, but with kernel 6.18 (2025 LTS kernel), not kernel 6.12 (2024 LTS kernel and the Trixie default). I expect TrueNAS 27 will still be Trixie but with the 2026 LTS kernel (7.4?), and then TrueNAS 28 might be Forky (Debian 14) with the 2027 LTS kernel.

(*) For the most part. There’s some shenanigans for ZFS and ofc GPU, but for most things, the drivers are in-tree.

24

So thanks a lot for the additional information.

So there is a chance that the problem is solved 2027.

25

I can reproduce a problem with the onboard Realtek RTL8125D rev 0c / XID 688 on current TrueNAS SCALE.

System:

  • TrueNAS SCALE 25.10.7
  • Kernel: 6.12.105-production+truenas
  • Motherboard: GIGABYTE B760 GAMING X DDR4 GEN5
  • CPU: Intel Core i5-12600K
  • Onboard NIC: Realtek RTL8125D, PCI revision 0c, XID 688
  • Driver: r8169
  • Firmware: rtl8125d-1_0.0.7
  • Network: 2.5GbE switch and Cat Ethernet cabling
  • Bridge br0 used by TrueNAS/VM networking

The onboard RTL8125D intermittently drops and renegotiates the Ethernet link when running at 2.5Gbps.

Forcing the onboard NIC to advertise only 1000baseT/Full makes the system stable.

To rule out the switch, cable, TrueNAS bridge, SMB configuration and the rest of the system, I installed a separate PCIe Realtek RTL8125B rev 05 NIC.

A/B comparison:

Onboard NIC:
06:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller [10ec:8125] (rev 0c)
Subsystem: Gigabyte Technology Co., Ltd RTL8125 2.5GbE Controller
Kernel driver in use: r8169
Detected by r8169 as RTL8125D, XID 688

Result:

  • intermittent Link Down / Link Up at 2.5Gbps
  • stable when limited to 1Gbps

PCIe replacement NIC:
05:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller [10ec:8125] (rev 05)
Kernel driver in use: r8169
Detected as RTL8125B

Result:

  • stable at 2500Mb/s Full Duplex
  • no link flaps after installation
  • iperf3 PC → TrueNAS: ~2.37 Gbit/s
  • iperf3 TrueNAS → PC: ~2.37 Gbit/s
  • single TCP stream also reaches ~2.37 Gbit/s
  • SMB real-world transfer reached ~289 MB/s
  • same cable
  • same switch port/network
  • same TrueNAS installation
  • same bridge
  • same r8169 driver

Therefore the physical network and general TrueNAS configuration appear to be healthy. The issue follows the RTL8125D rev 0c / XID 688 onboard controller.

There is already an upstream netdev report describing intermittent disconnects with RTL8125D XID 688:

There is also a recent upstream discussion specifically about RTL8125D/XID 688 behaviour at 2.5Gbps:
https://lists.openwall.net/netdev/2026/08/17/184

I would be happy to provide additional ethtool, journalctl, PCIe or debug output if useful.

I would strongly prefer fixing/supporting the onboard NIC rather than permanently consuming a PCIe slot with an additional network adapter.

26

You can try 26 Beta 3 and see if the issue is still there. I don’t know if the driver was updated. TrueNAS 27 would be the next version that may get a driver update.