Nortel Networks 8000 - Manual (Page 467)

12 PPPoE configuration
Nortel Secure Router 8000 Series
Configuration -WAN Access
12.1 Introduction
CD NOTE
On the SR8000, only the Ethernet interface of the low-speed card supports the PPPoE feature.
This section covers the following topics that you need to know before you configure PPPoE:
• Concept of PPPoE
• Phase of discovery
• Phase of PPP session
12.1.1 Concept of PPPoE
Point-to-Point Protocol over Ethernet (PPPoE) is widely used in fields such as residential area
networking.
PPPoE establishes networks with a number of hosts over the Ethernet accessing the internet
through a remote access device and performs access control and accounting on each host.
PPPoE can achieve very high performance-to-price ratio, which makes it widely used in fields
such as residential area networking.
For more information about PPPoE, refer to RFC2516.
PPPoE includes two phases: discovery and PPP session.
12.1.2 Phase of discovery
Before starting a PPPoE process, the host must identify the Ethernet MAC address of the
accessing terminal and create a session ID for PPPoE, which is the purpose of the Phase of
Discovery.
The Phase of Discovery consists of the following four steps:
• In the Ethernet, the host broadcasts a PPPoE Active Discovery Initial (PADI) packet,
which contains the service type information that the host wants to obtain.
CQ NOTE
• If you configure the service-name at the server side of PPPoE, the client sends a PADI packet to the
server, requesting for connection.
• If a non-null service name exists in the PADI packet, the server checks whether the configured
service name on it matches with that in the packet. If the two service names are found to be the same,
the server provides services for the client; otherwise, the server does not provide any service to the
client.
• If one of the service names is null, checking is not required and you can directly proceed according
to the planned procedures.
• After receiving the PADI packet, all the servers in the Ethernet compare the requested
services with the services they can offer. The servers that can provide this service send
back the PPPoE Active Discovery Offer (PADO) packet to this host.
• The host may receive more than one PADO packet from several servers. The host checks
the PADO packet it receives and chooses one server, based on certain conditions and
sends a PPPoE Active Discovery Request (PADR) packet (non-broadcast) to the server it
has chosen.
• The server generates a unique session identifier for this PPPoE session with the host, and
contains the identifier in the PPPoE Active Discovery Session-confirmation (PADS)
12-2 Nortel Networks Inc. Issue 5.3 (30 March 2009)