PPPoE allows Internet Service Providers to manage access to accounts via user names and passwords. DSL service providers began using PPPoE many years ago, as it proved a convenient technical solution for converting subscribers from dial-up Internet.
While convenient for service providers, some customers of PPPoE-based Internet service have experienced problems with their connection due to incompatibility between PPPoE technology and their personal network firewalls. Contact your service provider to verify whether they use PPPoE and get any assistance needed with your firewall settings.
The PPPoE protocol specification is Internet RFC 2516.
See also - MTU and PPPoE