Hello,

 

I have experimented with a Realtek USB 2.5Gbe USB Ethernet dongle and find that it works fine with the vendor kernel but not with kernels 6.12.x or 6.18.y. 

 

I have included an iperf3 example below, you can see that the dongle manages a few runs at high speed before it quietly fails and seizes up.

 

I use a number of these dongles and they tend to work fine on other set-ups.

 

Any thoughts about a resolution?

 

dmesg output:

[Tue Mar 17 11:37:00 2026] usb 2-1: new SuperSpeed USB device number 2 using xhci-hcd
[Tue Mar 17 11:37:00 2026] usb 2-1: New USB device found, idVendor=0bda, idProduct=8156, bcdDevice=31.00
[Tue Mar 17 11:37:00 2026] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=6
[Tue Mar 17 11:37:00 2026] usb 2-1: Product: USB 10/100/1G/2.5G LAN
[Tue Mar 17 11:37:00 2026] usb 2-1: Manufacturer: Realtek
[Tue Mar 17 11:37:00 2026] usb 2-1: SerialNumber: 0013000001
[Tue Mar 17 11:37:00 2026] usbcore: registered new device driver r8152-cfgselector
[Tue Mar 17 11:37:00 2026] r8152-cfgselector 2-1: reset SuperSpeed USB device number 2 using xhci-hcd
[Tue Mar 17 11:37:01 2026] r8152 2-1:1.0 eth0: v1.12.13
[Tue Mar 17 11:37:01 2026] usbcore: registered new interface driver r8152
[Tue Mar 17 11:37:01 2026] usbcore: registered new interface driver cdc_ether
[Tue Mar 17 11:37:01 2026] usbcore: registered new interface driver cdc_ncm
[Tue Mar 17 11:37:01 2026] usbcore: registered new interface driver cdc_wdm
[Tue Mar 17 11:37:01 2026] usbcore: registered new interface driver cdc_mbim
[Tue Mar 17 11:37:01 2026] r8152 2-1:1.0 enx00e04c680142: renamed from eth0
[Tue Mar 17 11:37:02 2026] xhci-hcd xhci-hcd.3.auto: WARN: HC couldn't access mem fast enough for slot 1 ep 6
[Tue Mar 17 11:37:02 2026] r8152 2-1:1.0 enx00e04c680142: intr status -63
[Tue Mar 17 11:37:07 2026] xhci-hcd xhci-hcd.3.auto: WARN: HC couldn't access mem fast enough for slot 1 ep 6
[Tue Mar 17 11:37:07 2026] r8152 2-1:1.0 enx00e04c680142: intr status -63
[Tue Mar 17 11:37:35 2026] xhci-hcd xhci-hcd.3.auto: WARN: HC couldn't access mem fast enough for slot 1 ep 6
[Tue Mar 17 11:37:35 2026] r8152 2-1:1.0 enx00e04c680142: intr status -63

Subsequent iperf3 example:
iperf3 -c nx1
Connecting to host nx1, port 5201
[  5] local 192.168.1.191 port 58598 connected to 192.168.1.14 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   221 MBytes  1.85 Gbits/sec    0   5.35 MBytes       
[  5]   1.00-2.00   sec   280 MBytes  2.35 Gbits/sec    0   5.35 MBytes       
[  5]   2.00-3.00   sec   280 MBytes  2.35 Gbits/sec    0   5.35 MBytes       
[  5]   3.00-4.00   sec  18.1 MBytes   152 Mbits/sec    1   1.41 KBytes       
[  5]   4.00-5.00   sec  0.00 Bytes  0.00 bits/sec    0   1.41 KBytes       
[  5]   5.00-6.00   sec  0.00 Bytes  0.00 bits/sec    0   1.41 KBytes       
[  5]   6.00-7.00   sec  0.00 Bytes  0.00 bits/sec    0   1.41 KBytes       
[  5]   7.00-8.00   sec  0.00 Bytes  0.00 bits/sec    0   1.41 KBytes       
[  5]   8.00-9.00   sec  0.00 Bytes  0.00 bits/sec    0   1.41 KBytes       
[  5]   9.00-10.00  sec  0.00 Bytes  0.00 bits/sec    0   1.41 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   800 MBytes   670 Mbits/sec    1            sender
[  5]   0.00-10.86  sec   796 MBytes   615 Mbits/sec                  receiver

 

This device is not yet fully compatible with the mainline Linux kernel. Realtek USB 2.5GbE adapters, in particular, are known to have issues when used over USB 3 on these devices. The vendor-provided kernel reportedly offers better tuning for these adapters, though it is still not entirely flawless.