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Network Configuration—PPPPoint-to-Point Protocol (PPP) is a layer2 protocol used to encapsulate layer3 traffic(that is IP) over a point-to-point physical medium, such as an asynchronous serialinterface. PPP was introduced in 1989 based on HDLC protocol and was extendedsubsequently, based on the need to support more protocols and extensions. Thelatest standard (RFC 1661) was updated in 1994. Numerous extensions have becomeavailable for the protocol since then, including authentication, compression, andcontrol protocols as well as some vendor-specific extensions.FreeBSD 7 supports PPP protocol in the base system (which means no third-partysoftware should be installed for normal usage).There are two implementations of PPP stack in FreeBSD which are known as UserPPP and Kernel PPP.As the names suggest, the User PPP does not engage kernel in the process of inboundand outbound traffic encapsulation. It uses an external process and a generic tunneldriver for PPP encapsulation. This implies lower performance as compared to KernelPPP, which uses codes in kernel for PPP encapsulation, but offers more features andflexibility over Kernel PPP.Another difference between these two implementations is that User PPP uses tun(4)device, while Kernel PPP uses the ppp(4) interface between lower layers andthe network.There are also two special (and important) implementations of PPP protocol that aresupported in FreeBSD—PPPoE and PPPoA.PPP over Ethernet (PPPoE, defined in RFC 2516) is a special version of PPPprotocols that encapsulates PPP frames inside Ethernet frames. It is mostly used onbroadband access networks (for example ADSL and Wireless) to provide a method toauthenticate and authorize users.