Point-to-Point Protocol (PPP)

PPP is used to transfer IP and other packet based traffic through a serial line. It can also be encapsulated over Ethernet with PPP-over-Ethernet (PPPoE) and over ATM with PPP-over-ATM (PPPoA); these are used by many ISP's (Internet Service Providers) for broadband Internet access.

Protocol dependencies

• PPP can run directly over a serial line (dial-up or directly-connected asynchronous lines and synchronous lines such as T1/E1 lines).
• ISDN: PPP can run over an ISDN B channel.
• Ethernet: PPP can use Ethernet and other protocols in the LanProtocolFamily with PPPoE.
• ATM: PPP can use ATM with PPPoA.

PPPoE is a network configuration used for establishing a PPP connection over an Ethernet protocol. It is commonly used for creating DSL Internet connections. Since DSL modems typically connect to computers via an Ethernet connection, a standard dial-up PPP connection cannot be used. Therefore, PPP over Ethernet allows computers to connect to an Internet service provider (ISP) via a DSL modem.

With PPPoE, users virtually “dial” from one machine to another over an Ethernet network, establish a point-to-point connection and then data packets are securely transported through the connection.

PPPoE is primarily used by telephone companies. The protocol allows for the easy separation of digital subscriber line access multiplexers (DSLAM) where it is required by regulators.

This process, also known as PPPoE discovery, involves the following steps:

1. Initiation - The client software sends a PPPoE Active Discovery Initiation (PADI) packet to the server to intitiate the session.
2. Offer - The server responds with a PPPoE Active Discovery Offer (PADO) packet.
3. Request - Upon receipt of the PADO packet, the client responds by sending a PPPoE Active Discovery Request (PADR) packet to the server.
4. Confirmation - Upon receipt of the PADR packet, the server responds by generating a unique ID for the PPP session and sends it in a PPPoE Active Discovery Session (PADS) confirmation packet to the client.

When a PPPoE session is initiated, the destination IP address is only used when the session is active. The IP address is released after the session is closed, allowing for efficient re-use of IP addresses.