Lenovo M910q with Realtek RTL8125 only 100Mbit/s

[uwe0480]

I have two Lenovo M910q systems and have installed a Realtek RTL8125 2.5GbE Controller in each one. The cards are directly connected with no switch in between.

lspci -v | grep Ethernet
00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (2) I219-LM Subsystem: Lenovo Ethernet Connection (2) I219-LM
02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller (rev 05)

Ethtool shows the correct device as well as link modes and advertised link modes.

ethtool enp2s0
Settings for enp2s0:
    Supported ports: [ TP     MII ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
                            2500baseT/Full
    Supported pause frame use: Symmetric Receive-only
    Supports auto-negotiation: Yes
    Supported FEC modes: Not reported
    Advertised link modes:  10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
                            2500baseT/Full
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Advertised FEC modes: Not reported
    Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                         100baseT/Half 100baseT/Full
    Link partner advertised pause frame use: Symmetric Receive-only
    Link partner advertised auto-negotiation: Yes
    Link partner advertised FEC modes: Not reported
    Speed: 100Mb/s
    Duplex: Full
    Auto-negotiation: on
    master-slave cfg: preferred slave
    master-slave status: slave
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: external
    MDI-X: Unknown
    Supports Wake-on: pumbg
    Wake-on: d
    Link detected: yes

lshw -class network
  *-network
       description: Ethernet interface
       product: RTL8125 2.5GbE Controller
       vendor: Realtek Semiconductor Co., Ltd.
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: enp2s0
       version: 05
       serial: 1c:fd:08:7a:ae:d6
       size: 100Mbit/s
       capacity: 1Gbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix vpd bus_master cap_list rom ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=6.2.16-8-pve duplex=full firmware=rtl8125b-2_0.0.2 07/13/20 ip=172.0.0.2 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
       resources: irq:17 ioport:e000(size=256) memory:f7010000-f701ffff memory:f7020000-f7023fff memory:f7000000-f700ffff

Unfortunately, even if the two network cards are identical, they only negotiate to 100Mb/s. I have changed network cables and tried ethtool -s enp2s0 speed 2500 duplex full to force full speed. It does not work and breaks the connection. I have also connected one card to my Unifi Switch to test the connection. The result is the same. The maximum speed is 100Mb/s. Does anyone has an idea?

 

[JensF]

You're sure that you're using standard patch cable? At least CAT5e (better CAT6) and NOT cross over cables!
The wire colors are the same on both plugs?

 

[uwe0480]

You're sure that you're using standard patch cable? At least CAT5e (better CAT6) and NOT cross over cables!
The wire colors are the same on both plugs?

I have used CAT7 cables which are installed throughout my entire network. Alternatively, I tested CAT6 cables from Ubiquity. Both with the same negative result. I have no idea, why all modes are fine, yet it only negotiates to the slow speed.

 

[JensF]

CAT7 is absolutely fine and should work. But could still be a connection problem.