My Ethernet adapter is somehow stuck at 10 Mbit/s. Here's the output of ethtool eth0:

Settings for eth0:
    Supported ports: [ TP MII ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Full 
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Link partner advertised link modes:  10baseT/Half 10baseT/Full 
                                         100baseT/Half 100baseT/Full 
    Link partner advertised pause frame use: Symmetric
    Link partner advertised auto-negotiation: Yes
    Speed: 10Mb/s
    Duplex: Full
    Port: MII
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    Current message level: 0x00000007 (7)
                   drv probe link
    Link detected: yes

As you can see, my adapter supports 100 Mbit/s, and the "link partner" (my router?) supports 100 Mbit/s. However, if I manually set the mode to 100 Mbit/s using sudo ethtool -s eth0 speed 100 duplex full the link immediately disconnects.

How can I fix this problem?

  • 1
    how do you know it is the adapter that is the problem? There are number of things that could be an issue....what other troubleshooting have you done? – mdpc May 8 '14 at 4:36
  • How did I imply it's the adapter that is the problem? – ithisa May 8 '14 at 5:19
  • 1
    Connect the pc to another router or switch. Or connect another pc to the router using your wire. – davidbaumann May 8 '14 at 5:28
  • Other PCs use 100MiB/s correctly :/ – ithisa May 8 '14 at 5:47
  • Can you post the output of ethtool -i eth0, dmesg | grep eth0, grep . /sys/class/net/eth0/device/{subsystem_,}{device,vendor} and udevadm info --export-db | awk -vRS= /eth0/ – Stéphane Chazelas May 8 '14 at 10:51

Have you tried (while the system is on) turning the interface off and on? I'll assume that you have rebooted your system and this is something consistently happening.

Use a different cable. Bad cables or connectors do happen. Also of note, make sure you are using the right Cat of cable.

Use a different router/switch port. The router/switch port might be bad.

Examine configuration of router/switch port, is it auto negotiating? is the speed fixed? If you try to do auto on a port that has a fixed speed, I have seen what you have specified happen.

Some adapter boards do not properly do auto negotiation. If that is the case, then manually set both the router/switch port to a fixed speed.

Finally replace adapter board with new board and go through the troubleshooting including above.

Your final option is that the switch/router is bad.

  • 1
    I've tried everything. I turned autonegotiating off: it dies whenever I manually set 100 MiB/s. I connected the cable to another PC; works at 100 MiB/s. I am beginning to suspect this is simply a shitty interface (I bought it at a cheap Chinese store; it doesn't even have a brand on it) that falsely advertises 100 MiB/s support to the OS. – ithisa May 8 '14 at 6:41
  • do you have access to the router/switch? You sound as if this is not the case, I'd advise working with the site systems admin to verify the router/switch configuration. – mdpc May 8 '14 at 6:42
  • Why are you assuming so many stuff? I am simply at home, and I can configure anything about the router, and control the entire network. – ithisa May 8 '14 at 8:42
  • without information in the question, I can only guess. – mdpc May 8 '14 at 18:09
  • BTW, looks like it is time to get a new timex (adapter board) from what you are saying. – mdpc May 8 '14 at 18:09

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