User's Manual

Table Of Contents
Configuration Guide of XGS-5240-Series
57-1
Chapter 57 PPPoE Intermediate Agent
Configuration
57.1 Introduction to PPPoE Intermediate Agent
57.1.1
Brief Introduction to PPPoE
PPPoE (Point to Point Protocol over Ethernet) is a protocol that apply PPP protoco
l to Ethernet. PPP protocol is a link layer protocol and supply a communication method
of point-to-point, it is usually selected by host dial-up link, for example the link is line
dial-up. PPP protocol is applied to Ethernet that means PPPoE protocol makes many h
osts of Ethernet to connect a remote access collector through one or multiple bridge d
evices. If the remote access collector is broadband access server (BAS), it can supply
broadband access and accounting functions for these hosts, so PPPoE protocol is used
to broadband access authentication of Ethernet usually.
57.1.2 Introduction to PPPoE IA
Along with broadband access technique is rapidly developed, broadband access net
work is also developing from strength to strength, but security problem gradually becom
es the focus, soever the clients or the access device and the network are faced with s
ecurity problem (especially from the client) in the current access network. Traditional Et
hernet user can not be identified, traced and located exactly, however in exoteric and c
ontrollable network, identification and location are the basic character and requirement f
or user, for example, when supplying the application that use user accounts to login, th
is method supplied by PPPoE Intermediate Agent can availably avoid user accounts em
bezzled.
There are two stages for PPPoE protocol work: discovery stage and session stage.
Discovery stage is used to obtain MAC address of the remote server to establish a p
oint-to-point link and a session ID with the server, and session stage uses this session
ID to communicate. PPPoE Intermediate Agent only relates to discovery stage, so we
simply introduce discovery stage.
There are four steps for discovery stage:
1. Client sends PADI packet: The first step, client uses broadcast address as des
tination address and broadcast PADI (PPPoE Active Discovery Initiation) packet
to discover access collector in layer 2 network. Notice: This message may be