Just after I installed Debian Squeeze, at first boot, the wired ethernet connection, which worked so well during the install, was not working in the X system (Gnome).
I wondered a lot trying to find an error in ifconfig or dmesg, but could find none. After a while, I noticed that the “status” of the connection in Gnome whenever I clicked on the network manager icon was:
“Wired device not managed”
The device was simply not activated in the interfaces!
In order to activate it, type from a terminal:
$ sudo emacs /etc/NetworkManager/NetworkManager.conf
(or ‘vi’ or ‘nano’ instead of emacs, depending on your favourite text editor)
Then change the line:
$ sudo service network-manager restart