What is PPPoE?

PPPoE (Point-to-Point Protocol Over Ethernet) is a network tunnel protocol which encapsulates the point-to-point protocol (PPP) in the Ethernet framework. Due to the integration of PPP protocol in the protocol, it realizes the authentication, encryption and compression functions that traditional Ethernet cannot provide, and can also be used in cable modems and digital subscriber line (DSL) protocol systems that provide access services to users via Ethernet protocol.

Essentially, it is a protocol that allows the creation of point-to-point tunnels between two Ethernet interfaces in the Ethernet broadcast domain.

Take the PPPD commonly used in Linux system as an example, whic supports IP, IPv6 and IPX network layer protocols over PPP interfaces.

It uses traditional PPP-based software to manage a connection that uses not a serial line but a directed packet network similar to Ethernet. This standard connection with login and password facilitates access to vendor billing. Also, the other end of the connection is assigned an IP address only when the PPPoE connection is made, allowing dynamic multiplexing of IP addresses.

PPPoE was developed by UUNET, Redback Networks and RouterWare.

Working principle of PPPoE

The working process of the PPPoE protocol consists of discovery and session stages, the discovery stage is stateless, and the purpose is to obtain the Ethernet MAC address of the terminal end of the PPPoE (on the local ADSL device), and to establish a unique PPPoE SESSION-ID.

When the discovery stage is over, the standard PPP session stage is entered.

When a host wants to start a PPPoE session, it must first go through the discovery stage to identify the Ethernet MAC address at the local end and establish a PPPoE SESSION-ID.

In the discovery stage, based on the network topology, the host can discover multiple access concentrators and then allow the user to select one. When the discovery stage is successfully completed, both the host and the selected access concentrator have the information they need to establish PPP connections on the Ethernet.

A client/server mode that remains stateless during the discovery stage until the PPP session is established.

Once a PPP session is established, both the host and the access concentrator must allocate resources for the PPP virtual interface.