Undo the settings of pppoeconf command

"pppoeconf" sets up dialup networks on linux/ connect to internet without connecting via network manager. But thats done, it sets up few files to always do that.
To undo this on ubuntu, follow these steps :

1) Edit nm-system-settings.conf

vim /etc/NetworkManager/nm-system-settings.conf


You have to write managed=true under [ifupdown]

4) Edit interfaces

vim /etc/network/interfaces


This file must look like this:

auto lo
iface lo inet loopback

auto eth0
iface eth0 dhcp


5) Restart your computer

reboot


6) Finished.