The ncurses utility PPPoE/ADSL - PPP over ethernet driver. pppoeconf Configures PPP/ADSL connections.
Using pppoeconf
Tested and successful on a Mint 19.2 system, provides the ability to connect to a bridge mode router and provide PPPoE authentication to the ISP.
You can install it
sudo apt install pppoeconf
Running 'pppoeconf' from the command line will prompt the user for a sudo user password. Accepting defaults and providing the correct username and password will work for most people.
pppoe clamp MSS at 1452 bytes (If you still get problems described above try setting to 1412 in the dsl-provider file.) Now, you can make a DSL connection with "pon dsl-provider" and terminate it with "poff". You can use the "plog" command to see the status or "ip addr show ppp0" for general interface info.
Undo and Reverse Changes to your Linux Mint system after using pppoeconf
The pppoeconf utility was tested and used successfully on a Linux Mint 19.2 installation with a PC that had a wired Ethernet controller and a Wireless controller also. The wireless controller is not relevant to this example.
The owner of the system no longer needed to use pppoeconf on the system after purchasing a router/firewall appliance. However, it was no longer possible to configure the network settings from the Mint applet.
To remove pppoeconf from the system
sudo apt-get remove pppoeconf sudo apt-get autoremove pppoeconf sudo apt-get purge pppoeconf
After a reboot the wired interface appears in the "Network Connections" applet and the interface also appears in 'ifconfig'. However, the interface is still not visible in the "Network" applet, this is the one that lets you toggle the connection on and off by clicking. Although 'ifconfig -a' shows the Ethernet interface, the Mint Network Connections applet no longer is able to modify the configuration. It is simply ignored.
Next step: In Linux Mint 19.2 the file /etc/network/interfaces was modified by pppoeconf
sudo vi /etc/network/interfaces
Remove all the stuff added by pppoeconf. This is pretty much anything after the 4th line.
For most people you should only have the following in the /etc/network/interfaces file:
# interfaces(5) file used by ifup(8) and ifdown(8) auto lo iface lo inet loopback
After a reboot the standard Mint Network applet will show the device and Network Connections will allow configuration once again. This essentially restores the system using the mint alternative configuration rather than the traditional configuration that one might find on a pure Debian system. Mint does the same messing around with standards that Ubuntu does in the case, just differently in their own minty way.