I have a 2.5GBps NIC: RTL8125B which did not work out-of-box. It would not even show up in lspci.
After installing r8168-dkms package, and rebooting, I was able to use it for a week or so.
Today, the NIC stopped working. The kernel sees no device, and lspci doesn't see it either.
I purged the r8168-dkms package, reinstalled it, and rebooted, which did not work.
I have a second machine with the same NIC, running the same Ubuntu version, and same r8168-dkms package.
That machine still sees the NIC, but it uses the r8169 driver to do so.
I am also surprised that lspci will not list the device. Does lspci rely on drivers for that?
The lshw tool does not see it either as lshw -C network will only show my Intel NICs.
OS: Ubuntu 21.04
Kernel: 5.11.0-17-generic #18-Ubuntu SMP
r8168-dkms: 8.048.03-3
UPDATE:
Rebooting did not help, but an actual power-off by physically switching off the PSU, did help.
The system is a Xeon on a Supermicro X11-SRM-F server board, using IPMI, so maybe a reboot is not always a full reboot? It is unclear to me why a physical switching off resets more than a reboot?
After manual powercycle, I get:
65:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller (rev 04)
Subsystem: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller
Flags: bus master, fast devsel, latency 0, IRQ 40, NUMA node 0
I/O ports at b000 [size=256]
Memory at e0e10000 (64-bit, non-prefetchable) [size=64K]
Memory at e0e20000 (64-bit, non-prefetchable) [size=16K]
Expansion ROM at e0e00000 [disabled] [size=64K]
Capabilities: [40] Power Management version 3
Capabilities: [50] MSI: Enable- Count=1/1 Maskable+ 64bit+
Capabilities: [70] Express Endpoint, MSI 01
Capabilities: [b0] MSI-X: Enable+ Count=32 Masked-
Capabilities: [d0] Vital Product Data
Capabilities: [100] Advanced Error Reporting
Capabilities: [148] Virtual Channel
Capabilities: [168] Device Serial Number 01-50-00-00-b0-b3-c9-88
Capabilities: [178] Transaction Processing Hints
Capabilities: [204] Latency Tolerance Reporting
Capabilities: [20c] L1 PM Substates
Capabilities: [21c] Vendor Specific Information: ID=0002 Rev=4 Len=100 <?>
Kernel driver in use: r8169
Kernel modules: r8169
UPDATE
$ sudo modprobe r8125 && sudo dmesg | grep r81
modprobe: FATAL: Module r8125 not found in directory /lib/modules/5.11.0-17-generic