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many access collector of the network.
2.
Broadband Access Server responds PADO packet: The second step, server
responds PADO (PPPoE Active Discovery Offer) packet to client according to the
received source MAC address of PADI packet, the packet will take sever name and
service name.
3.
Client sends PADR packet: The third step, client selects a server to process the
session according to the received PADO packet. It may receives many PADO
packets for PADI message of the first step may be sent to many servers (select the
server according to whether the service information of PADO packet match with the
servce information needed by client). MAC address of the other end used for session
will be known after server is selected, and send PADR (PPPoE Active Discovery
Request) packet to it to announce server the session requirement.
4.
Server responds PADS packet: The fourth step, server establishes a session ID
according to the received PADR packet, this session ID will be sent to client through
PADS (PPPoE Active Discovery Session-confirmation) packet, hereto PPPoE
discovery stage is completed, enter session stage.
PADT (PPPoE Active Discovery Terminate) packet is an especial packet of PPPoE, its'
Ethernet protocol number (0x8863) is the same as four packets above, so it can be considered
a packet of discovery stage. To stop a PPPoE session, PADT may be sent at the discretional
time of the session. (It can be sent by client or server)
PPPoE Intermediate Agent supplies a function that identify and locate the user. When passing
network access device, PADI and PADR messages sent by client with the access link tag of
this device at PPPoE discovery stage, so as to exactly identify and locate the user on server.
If the direct-link access device is LAN switch, the added information include: MAC, Slot ID,
Port Index, Vlan ID, and so on. This function is implemented according to Migration to
Ethernet-based DSL aggregation.
51.1.2.1 PPPoE Intermediate Agent Exchange Process
PPPoE Intermediate Agent exchange process is similar to PPPoE exchange process, for the
first exchange process, the access link tag is added to PADI and PADR packets. The
exchange process is as follows:
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