PLANET XGS3-24042 - Manual (Page 567)

61-11
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.
61.1.2.1 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:
Figure 61-1 PPPoE IA protocol exchange process
61.1.2.2 PPPoE Packet Format
PPPoE packet format is as follows:
Ethernet II frame
Destination MAC Source MAC Type Field PPPoE Data CRC Check Sum