To use my Lenovo Thinkpad L450 as a notebook and desktop computer at the same time, I ordered a Lenovo ThinkPad Ultra Dock. This dock provides all needed connectors (USB, HDMI, VGA, DVI, power, LAN, audio) which means I can connect all my devices (mouse, keyboard, router, speakers, external monitor, …) to the dock and when I want to use the Thinkpad as desktop PC, I just dock it and do not need to plug all the cables every day again.
The dock works fine, but there was a strange problem when using the ethernet port of the dock. When I used the notebook on the dock (and the dock was connected to my FritzBox 7360SL router via ethernet), I had random connection loss over the time. These connection problems seemed to occur more often when I downloaded big files (=> increased traffic). I am using Ubuntu 14.04.
My syslog told me:
[ 1098.056242] e1000e: eth0 NIC Link is Down
[ 1107.800628] e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 1107.800631] e1000e 0000:00:19.0 eth0: 10/100 speed: disabling TSO
A few seconds after the connection was lost, it reconnected automatically.
First, I tried to use a new cable which didn’t help. Then I tried to disable WLAN when using the notebook on the dock. This also had no effect on the problem. My next try was to use the latest stable kernel that was available for Ubuntu 14.04 (Linux 4.4). Unfortunately, this also did not solve the problem.
I wondered what caused the problems and opened the configurations menu of my router (http://fritz.box) and navigated to „Home network“ => „Network“ => „Network settings“. There’s a table showing all four LAN ports of the router and it showed that LAN 1 & 2 worked in the „Power Mode“ (1Gbit/s) and LAN 3 & 4 worked in the „Green Mode“ (100Mbit/s). The dock was connected to one of the „Green Mode“ ports. So I tried to use one of the Power Mode ports instead and it really worked!
I had no connection loss since I connected it to one of the „Power Mode“ ports. So I think, there is a problem with the „Green Mode“ in my Fritz!Box 7360SL router that causes the connection to drop randomly. Maybe the signal isn’t strong enough? I don’t know… I thought the only difference between the power mode and the green mode was the connection speed (1Gbit/s vs 100Mbit/s) but there seem to be more differences which cause the problems.
If someone knows what exactly could be the problem, please let me know in the comments section!