Ubuntu ADSL dial-up Internet time and time continuous problem

When you use pppoeconf, you may have a disconnected network link and the network Manager display device is unmanaged. The reason is that NetworkManager is in conflict with the networking command and cannot be mixed. If you experience this problem, try:

1. Run in Terminal:
sudo mv/etc/network/interfaces/etc/network/interfaces_backup

2. Remove DNS settings: sudo mv/etc/resolv.conf/etc/resolv.conf_backup

3. Restart Network-manager services: sudo service Network-manager restart

Reference: 1. [Learn]ubuntu adapter eth0 and other 2. Ubuntu 9.10 inability to ADSL dial-up and network Manager display device unmanaged solution