I run Ubuntu Desktop on my machine at work, and for years I’ve had trouble with the network connection. It seems that our IT department is… deficient. To keep a long story short, the switches they have installed have lots of problems with auto negotiation. Sometimes, you only get 10Mb/s instead of 100Mb/s (don’t even ask about 1000Mb/s). Other times, you might get 100Mb/s only to find out you are operating at half duplex.
The fix for these issues is to run the command
ethtool -s ethX autoneg off duplex full speed 100
On server installations, you can simply put this in the post-up part of /etc/network/interfaces.
On desktops though, it is better to put them in a script that Network Manager can use.
From the man pages
NetworkManager will execute scripts in the /etc/NetworkManager/dis‐
patcher.d directory in alphabetical order in response to network
events. Each script should be:
(a) a regular file
(b) owned by root
(c) not writable by group or other
(d) not set-uid
(e) and executable by the owner
Each script receives two arguments, the first being the interface name
of the device just activated, and second an action.
The actions are up, down, vpn-up, vpn-down, hostname, and dhcp4-change.
Thus, the following script placed in /etc/NetworkManager/dispatcher.d/fixspeed.sh will run the magic network fixing command.
#!/bin/bash
if [ "$1" = "eth0" ] && [ "$2" = "up" ]; then
ethtool -s eth0 autoneg off speed 100 duplex full
fi
exit $?