PPPoE Facts

PPPoE or Point-to-Point Protocol over Ethernet is a network protocol for encapsulation of PPP (Point-to-Point Protocol) frames inside the Ethernet frames.

Ethernet is made up of different computer networking technologies which are commonly used in LANs (local area networks) and MANs (metropolitan area networks). It was commercially introduced for the first time in 1980, and was later standardized in 1983 in the form of an IEEE 802.3. Thereafter, it underwent several refinements for supporting longer link distances and higher bit rates.

The first time that PPPoE was implemented was in early 2000s when the DSL industry was in the stage of boom. It was the most preferred solution for tunneling of packets over DSL connections to their respective ISPs IP networks, and from thereon to the entire Internet. A networking book published in the year 2005 had noted that a large majority of DSL providers employed PPPoE as it provided encryption, authentication and compression.

The normal usage of PPPoE protocol involves making full use of the conventional PPP facilities for authentication of users with their usernames and passwords, less frequently with CHAP (challenge handshake authentication protocol, wherein a user or a network host is authenticated to an authenticating entity like an ISP) and predominantly through the PAP protocol.

Coming to the client side of its implementation, PPPoE can get implemented at the customer premises either through a unified residential gateway device handling both the IP routing and DSL modem functionalities; or if it’s a simple DSL modem that doesn’t provide any routing support, the PPPoE can be handled behind the scenes directly on the users’ computers (with inherent support functions of operating systems like Mac OS X, GNU/Linux, Windows XP etc.) or via separate Ethernet only routers). In fact, it’s not only the DSL-based, but also some GPON-based residential gateways that employ PPPoE these days. However, the PPPoE status in GPON standards is only marginal.

The people behind successful development and implementation of PPPoE were RouterWare (the Wind River Systems of today), Redback Networks (the Ericsson of today) and UUNET. The protocol is available in the form of an informational RFC 2516.

Talking about the DSL world, PPPoE was always believed to be running over the DSL’s ATM (Asynchronous Transfer Mode, a telecommunications concept defined by ITU and ANSI standards for carrying a comprehensive range of user traffic-types including video, data and voice signals) in the form of underlying transport, despite no such limitations existing in the protocol per se.

Other usage scenarios of PPPoE are distinguished by its tacking in the form of a suffix in some other underlying transport. For instance, in cases where the transportation medium is Ethernet itself, it is PPPoEoE, as can be seen in Metro Ethernet networks. Here the PPPoE protocol is labelled as PPPoEoA (not to be confused with another encapsulation protocol PPPoA).

Many technical books describe PPPoE as a layer 2.5 protocol, quite similar to the MPLS (Multiprotocol Label Switching, a kind of data-carrying method meant for high performance telecommunication networks wherein data is directed from one network node to another not based on the long network addresses but short path labels) since it can be employed for distinguishing between different IP flows sharing the same Ethernet infrastructure. However, the absence of PPPoE switches that make the routing decision depending on the PPPoE headers, limits its relevance in that aspect.