UTT Technologies
Chapter 7 Advanced
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Page 92
broadcasts a PADI packet to find all the servers that can be connected possibly. Until
it receives PADO packets from one or more servers. The PADI packet must contain a
service name which indicates the service requested by the client.
2.
PADO (PPPoE Active Discovery Offer):
When a PPPoE server receives a PADI
packet in its service range, it will send a PADO response packet. The PADO packet
must contain the server’s name, and a service name identical to the one in the PADI,
and any number of other service names which indicate other services that the PPPoE
server can offer. If a PPPoE server receives a PADI packet beyond its service range,
it cannot respond with a PADO packet.
3.
PADR (PPPoE Active Discovery Request):
The client may receive more than one
PADO packet as the PADI was broadcast. The client chooses one server according
to the server’s name or the services offered. Then the client sends a PADR packet to
the selected server. The PADR packet must contain a service name which indicates
the service requested by the client.
4.
PADS (PPPoE Active Discovery Session- confirmation):
When a PPPoE server
receives a PADR packet; it prepares to begin a PPP session. It generates a unique
PPPoE session ID, and respond to the client with a PADS packet. The PADS packet
must contain a service name which indicates the service provided to the client.
When the discovery stage completes successfully, both the server and client know the
PPPoE session ID and the peer's Ethernet MAC address, which together define the
PPPoE session uniquely.
6.4.1.3 PPP Session Stage
In the PPP session stage, the server and client perform standard PPP negotiation to
establish a PPP connection. After the PPP connection is established successfully, the
original datagram are encapsulated in PPP frames, and PPP frames are encapsulated in
PPPoE session frames, which have the Ethernet type 0x8864. Then these Ethernet
frames are sent to the peer. In a PPPoE session frame, the session ID must be the value
assigned in the Discovery stage, and cannot be changed in this session.
6.4.1.4 PPPoE Session Termination
After a session is established, either the server or client may send a PADT (PPPoE Active
Discovery Terminate) packet at anytime to indicate the session has been terminated. The
PADT packet’s SESSION-ID must be set, to indicate which session is to be terminated.
Once received a PADT, no further PPP packets (even normal PPP termination packets)
are allowed to be sent using the specified session. A PPP peer should use the PPP
protocol itself to terminate a PPPoE session, but can use the PADT packet to terminate
the
PPPoE
session
if
PPP
cannot
be
used.
