IPFire and Centurylink Fiber
I recently switched from pfSense to https://www.ipfire.org and got to learn the hoops needed for PPPoE over a vlan like Centurylink needs.
In IPFire this is considered a VDSL connection and isn’t available during the guided setup. But overall it's a pretty easy process. You'll need your PPPoE username and password from centurylink to get started.
During initial setup select the Dialup option (even though you are on Fiber :) ).
Go ahead with the rest of the setup, you'll finish up later.
After restarting and logging into the device via your browser go to System->Dialup
Then switch the type to VDSL and fill out as follows:
That's it. Go back to the main page System->Home and you'll see the connection there (if not, wait a few seconds and refresh the page).