RFC 2516 (rfc2516) - Page 2 of 17

A Method for Transmitting PPP Over Ethernet (PPPoE)

RFC 2516             Transmitting PPP Over Ethernet        February 1999


   This document describes the PPP Over Ethernet encapsulation that is
   being deployed by RedBack Networks, RouterWare, UUNET and others.

1. Introduction

   Modern access technologies are faced with several conflicting goals.
   It is desirable to connect multiple hosts at a remote site through
   the same customer premise access device.  It is also a goal to
   provide access control and billing functionality in a manner similar
   to dial-up services using PPP.  In many access technologies, the most
   cost effective method to attach multiple hosts to the customer
   premise access device, is via Ethernet.  In addition, it is desirable
   to keep the cost of this device as low as possible while requiring
   little or no configuration.

   PPP over Ethernet (PPPoE) provides the ability to connect a network
   of hosts over a simple bridging access device to a remote Access
   Concentrator.  With this model, each host utilizes it's own PPP stack
   and the user is presented with a familiar user interface.  Access
   control, billing and type of service can be done on a per-user,
   rather than a per-site, basis.

   To provide a point-to-point connection over Ethernet, each PPP
   session must learn the Ethernet address of the remote peer, as well
   as establish a unique session identifier.  PPPoE includes a discovery
   protocol that provides this.

2. Conventions

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [2].

3. Protocol Overview

   PPPoE has two distinct stages.  There is a Discovery stage and a PPP
   Session stage.  When a Host wishes to initiate a PPPoE session, it
   must first perform Discovery to identify the Ethernet MAC address of
   the peer and establish a PPPoE SESSION_ID.  While PPP defines a
   peer-to-peer relationship, Discovery is inherently a client-server
   relationship.  In the Discovery process, a Host (the client)
   discovers an Access Concentrator (the server).  Based on the network
   topology, there may be more than one Access Concentrator that the
   Host can communicate with.  The Discovery stage allows the Host to
   discover all Access Concentrators and then select one.  When
   Discovery completes successfully, both the Host and the selected
   Access Concentrator have the information they will use to build their
   point-to-point connection over Ethernet.



Mamakos, et. al.             Informational