In this case, your router talks PPP to the provider directly.
But first, the router puts this data into Ethernet frames which it transmits to the modem. (hence PPP-over-Ethernet)
Since the modem is in bridge-mode, it won't interpret the frames, only encapsulate them itself in AAL (ATM Adaption Layer) or whatever in order to transmit over the public network to the provider.
The provider then authenticates you etc.pp.
Other cases:
- "half-bridging": the modem performs the PPP authentication for you but doesn't do natting or anything but forwards the Ethernet traffic to an internal host/router which is supposed to do the rest
- Finally, the modem can also assume the role of a router, in which it does the PPP, NATting/routing, etc.
For your home router to establish a WAN connection to your ISP, a few things specific to PPP must happen first.
You may also have to do some research on LCP and NCP.
Check this link below, it may have the answer you are looking for (see the excerpt on PPPoE below):
https://infoproducts.alcatel-lucent.com/html/0_add-h-f/93-0098-09-01/7750_SR_OS_Triple_Play_Guide/concepts_PPPoE.html
PPPoE has two phases, the discovery phase and the session phase.•
Discovery: The client identifies the available servers.
To complete the phase the client and server must communicate a session-id. During the discovery phase all packets are delivered to the PPPoE control plane (CPM or MDA). The IOM identifies these packets by their ethertype (0x8863).
→ PPPoE Active Discovery Initiation (PADI). This broadcast packet is used by the client to search for an active server (Access Concentrator) providing access to a service.
→ PPPoE Active Discovery Offer (PADO): If the access server can provide the service it should respond with a unicast PADO to signal the client it may request connectivity. Multiple servers may respond and the client may choose a server to connect to.
→ PPPoE Active Discovery Request (PADR): After the client receives a PADO it will use this unicast packet to connect to a server and request service.
→ PPPoE Active Discovery Session-confirmation (PADS) A server may respond to the client with this unicast packet to establish the session and provide the session-id. Once the PADS was provided the PPP phase begins.
• Session: Once the session ID is established connectivity is available for the duration of the session, using ethertype 0x8864. Either client or server can terminate a session.
During the life of the session the packets may be uniquely identified by the client’s MAC address and session-id. The session can terminate either by PADT sent by the client or server or by an LCP Terminate-Request packet.
Best Answer
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.