pppoe-server is a systemd service which will allow you to start/stop the PPPoE Server on a specific interfaces.
The service is composed from 3 files:
/lib/systemd/system/pppoe-server@.service
/etc/default/pppoe-server
/usr/sbin/pppoe-server-config
The script pppoe-server-config will take the variables from /etc/default/pppoe-server will create a folder in /var/run/pppoe-server/ and it will create a pppoe-server.ses file. This file tracks all sessions for daemons.
Because for each interface we have to start a daemon the sessions must not overlap.
This file will keep a track for free sessions and also for used sessions and each time when a new daemon is started the script will return the necessary arguments for pppoe-server daemon.
Using the variables from the /etc/default/pppoe-server you can increase or decrease the number of the sessions per interface and also the total number of daemons.
Attention! If you change number of sessions and/or total number of daemons, please STOP all daemons, delete the file /var/run/pppoe-server/pppoe-server.ses and restart the daemons!
Also this script, if PPPOE_KERNELMODE is set in "auto", will try to find out if the PPPoE was build with kernel-mode support or not. This is important if you want to offload your CPU and move the PPPoE decapsulation into the kernel instead the userspace!