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 :) ).PPP Dialup sets things up mostly right
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).