A PPPoE session is always initiated by the PPPoE client. It will attempt to re-establish the connection if the session has a time-out or is disconnected. the following four steps occure during the Discovery stage:
The client broadcasts a PPPoE Active Discovery Initiation (PADI) packet.
If an access concentrator receives a PADI that it can serve, it replies by sending a PPPoE Active Discovery Offer (PADO) packet to the client.
Because the PADI was broadcast, the host may receive more than one PADO packet. The host looks through the PADO packets it receives and chooses one. The choice can be based on the access concentrator name or on the services offered. The host then sends a single PPPoE Active Discovery Request (PADR) packet to the access concentrator that it has chosen.
The access concentrator responds to the PADR by sending a PPPoE Active Discovery Session-confirmation (PADS) packet. At this point a virtual access interface is created that will then negotiate PPP, and the PPPoE session will run on this virtual access.
There is another packet type which can be sent to indicate that the PPPoE session has been terminated. Either the Client or the Access Concentrator can send the PPPoE Active Discovery Terminate (PADT) packet at any time after the session is established. When a PADT packet is received, no further PPP traffic is allowed to be sent using that session. A PPP peer should use the PPP protocol itself to bring down a PPPoE session, but the PADT may be used when PPP can not be used.
SNT after PADI just means Ethernet is admin shutdown.