The new Realtek r8168/r8111 network cards do not work out of the box in recent distributions of GNU/Linux. The "modprobe" loads the r8169 module, which has not yet been updated to work with these cards. A work around is to use the r8168 driver provided by Realtek.
Jameson Williams provides a shell script to automate the module switching:
http://www.jamesonwilliams.com/hardy-r8168