What is PPPoE?
Why would PPPoE be used?
Will there be any changes to how I use my High Speed Service?
Will there be a speed difference if my ISP switches to PPPoE?
Will PPPoE affect any Internet applications, such as ICQ?
Does PPPoE increase security risks with my broadband connection?
What is PPPoE:3Com (Or what has 3Com done to the PPPoE protocol)?
Is AOL PPPoE different?
What network interface does PPPoE require?
Can PPPoE be made to connect on boot for my PC?
How does PPPoE give me an IP address?
Can you explain the PPPoE discovery stage?

What is PPPoE?
Point to Point Protocol over Ethernet is a proposal specifying how a host personal computer (PC) interacts with a broadband modem (i.e. xDSL, cable, wireless, etc) to achieve access to the growing number of High speed data networks. Relying on two widely accepted standards, Ethernet and the point-to-point protocol (PPP), the PPPoE implementation requires virtually no more knowledge on the part of the end user other than that required for standard Dial up Internet access. In addition, PPPoE requires no major changes in the operational model for Internet Service Providers (ISPs) and carriers. The significance of PPP over Ethernet has to do with its far greater ease of use versus competing approaches. By making high speed access easier to use for end consumers, and more seamless to integrate into the existing infrastructure for carriers and ISPs, PPPoE could speed the widespread adoption of High speed access services

Also, PPP over Ethernet provides a major advantage for service providers by maximizing integration with - and minimizing disruption of - service providers' existing dial network infrastructures. Through tight integration with existing back office automation tools that ISPs have developed for dial customers, PPPoE enables rapid service deployment and cost savings. From authentication, accounting and secure access to configuration management, PPPoE supports a broad range of existing applications and services.

The base protocol is defined in RFC 2516.

Why would PPPoE be used?
PPPoE is used to allow Internet Service Providers (ISPs) the use of their existing Radius authentication systems from their Dial-Up service on a Broadband / Ethernet based service. Dial-Up is PPP, most broadband connections are Ethernet, hence Point to Point Protocol over Ethernet. It also allows for ISPs to resell the same line multiple times. IE: Rated services, Broadband specific content (movies, etc.), metered services, etc.

Will there be any changes to how I use my High Speed Service?
Instead of having the connection automatically occur when your computer boots (using DHCP for example to obtain an IP address), you would have to connect using PPPoE software like WinPoET, or maybe a router that will handle it for you. Once you are "connected" using the client, your connection will look / feel the same as your current connection. When you are finished, or when you've been idle for an undisclosed period of time, the client software may disconnect you and you will need to reconnect to gain access to the Internet again.

Will there be a speed difference if my ISP switches to PPPoE?
This is a difficult question to answer. The definition of the protocol points to a 5-10% decrease in bandwidth, as extra data will need to be sent down the line to handle the PPPoE signaling. There may be other penalties as well, derived from the server-side implementation.
If you look at this from a mathematical stand point PPPoE adds 8 bytes of header to the standard 1500 byte MTU packet. With this in mind you are only reducing speed by .3% (Yes .3 of one percent). So will you see a speed decrease, no, you probably won't.

Will PPPoE affect any Internet applications, such as ICQ?
The protocol has been out now and in use for, over 5 years. All internet apps can now be made to work with PPPoE.

Does PPPoE increase security risks with my broadband connection?
No in fact it will lower them. You can have your PC up and running but not connected to your ISP if you choose to disconnect with your PPPoE Software leaving you no longer vulnerable to and "Internet Attacks"

What is PPPoE:3Com (Or what has 3Com done to the PPPoE protocol)?
Simply put 3Com has created a proprietary version of the PPPoE protocol. It is only used when your 3Com DSL modem is set to PPPoA mode. When this happens it speaks PPPoA to your ISP, but then speaks PPPoE to your computer (That is why they bundle a PPPoE client with their DSL modems).
3Com has changed these two values:
ETHER_TYPE value for PPPoE Discovery phase: Changed from 0x8863 to 0x3c12
ETHER_TYPE value for PPPoE Session phase: Changed from 0x8864 to 0x3c13
Will this effect the use of a router? Yes. A few routers now support this new version only used with 3Com DSL modems in PPPoA mode.

Is AOL PPPoE different?
Originally AOL was using a proprietary version of a PPPoE application called WinPoET. This is no longer the case they are using their on PPPoE application but it is “standards” compliant.

What network interface does PPPoE require?
PPPoE applications require an Ethernet adapter with TCP/IP bound to it. This could be an Ethernet card, a USB to Ethernet adapter or simple a USB DSL modem.

Can PPPoE be made to connect on boot for my PC?
Most PPPoE applications such as WinPoET do have the feature to connect on Windows Startup

How does PPPoE give me an IP address?
Basically, when you click connect on your PPPoE application or when your router begins to connect to your ISP a discovery process occurs to ask for a connection. A session is then created. Your userid and password is then authenticated via Radius. Your IP, DNS, etc is the assigned via a process similar to DHCP (IPCP).

Can you explain the PPPoE discovery stage?
The PPPoE Discovery Stage is made up of four steps: initiation, offer, request, and session confirmation:

1)The PPPoE Active Discovery Initiation (PADI) packet:
The PPPoE client sends out a PADI packet to the broadcast address. This packet can also populate the "service-name" field if a service name has been entered on the dial-up networking properties of the PPPoE broadband connectoid. If a service name has not been entered, this field cannot be populated.

2) The PPPoE Active Discovery Offer (PADO) packet:
The PPPoE server, or Access Concentrator, should respond to the PADI with a PADO if the Access Concentrator is able to service the "service-name" field that had been listed in the PADI packet. If no "service-name" field had been listed, the Access Concentrator should respond with a PADO packet that has the "service-name" field populated with the service names that the Access Concentrator can service. The PADO packet is sent to the unicast address of the PPPoE client.

3) The PPPoE Active Discovery Request (PADR) packet:
When a PADO packet is received, the PPPoE client responds with a PADR packet. This packet is sent to the unicast address of the Access Concentrator. The client may receive multiple PADO packets, but the client responds to the first valid PADO that the client received. If the initial PADI packet had a blank "service-name" field filed, the client populates the "service-name" field of the PADR packet with the first service name that had been returned in the PADO packet.

4) The PPPoE Active Discovery Session-confirmation (PADS) packet:
When the PADR is received, the Access Concentrator generates a unique session identification (ID) for the Point-to-Point Protocol (PPP) session and returns this ID to the PPPoE client in the PADS packet. This packet is sent to the unicast address of the client.