Point-to-Point Protocol over Ethernet (PPPoE)

What is PPPoE?

Point-to-Point Protocol over Ethernet (PPPoE) is a network protocol which encapsulates PPP frames inside Ethernet. With PPPoE, multiple hosts in an Ethernet LAN are connected to the Provider Network and throughout this network, they connect Internet. Here, this connection is done over DSL and users share this DSL connection. By doing this, Point-to-Point Protocol over Ethernet provides a secure connection by establishing Point to Point connection over Ethernet technology. Connecting many users to their network over PPPoE technology is very useful and cost effective for Providers. PPPoE works as Client/Server system, there is a PPPoE Client and PPPoE Server.  

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  Point-to-Point Protocol over Ethernet is a Client / Server protocol. For the operation of Point-to-Point Protocol over Ethernet, firstly a Session must be established between PPPoE Client and PPPoE Server.

In this connection, the devices in the LAN are connected to PPPoE Client. This client is the Local Router of the user in a home network or in enterprise network. It is connected to Provider router network via DSLAM. Here, the Provider router is PPPoE Server. Throughout the Provider Router, Clients reach Internet.  

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PPPoE Session Establishment Stages

Point-to-Point Protocol over Ethernet has three stages. These Stages are :

1. Discovery Stage
2. Session Stage
3. Termination Stage

  Let’s check these stage one by one.  

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PPPoE Discovery Stage

The first Stage, the Discovery stage, is the stage in which the PPPoE Client discovers the availabile PPPoE Servers, their MACs and determine one of them to establish a PPPoE session.   In PPPoE Discovery stage there are four messages. These messages are orderly given below:

• PADI
• PADO
• PADR
• PADS

  PADI is the initialization message sent by the Client as broadcast to discover if are there any Server. PADO is the answer of the Servers available as unicast to the requested Client. PADR is the selection message of Client. This message is sent to the selected Server. PADS is the set up message sent by Server. Session ID is sent in this last stage and the Session is established.    

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PPPoE Session Stage

The second Stage, PPPoE Session Stage is the stage after session establishment at the disccovery stage . Here, PPP negotiation and transmission jobs are done.   The sub phases in Session Stage are given below:

• LCP Phase
• Authentication Phase
• NCP Phase

  In LCP (Link Control Protocol) Phase, a data link is established between PPPoE Client and Server. In Authentication Phase, some Authentication protocols like CHAP, PAP is used for authentication. In NCP (Network Control Protocol) Phase, IP Address configuration is done with IPCP.  

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PPPoE Termination Stage

The last stage is Termination Stage. In this stage PADT message is used. With PATD, PPPoE session is terminated. This message can be sent by both Client and PPPoE Server.  

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PPPoE Packet Format

Point-to-Point Protocol over Ethernet is the technology that PPP packets are encapsulated and transfered over Ethernet. Below, you can find the Ethernet Packet and PPPoE Packet that is eancapsulated in Ethernet Packet.   Here, in the data section of Ethernet sontains PPPoE Packet. And the data section of PPPoE Packet contains PPP Packet.