230Configuring PPPAbout PPPPoint-to-Point Protocol (PPP) is a point-to-point link layer protocol. It provides user authentication,supports synchronous/asynchronous communication, and allows for easy extension.PPP protocolsPPP includes the following protocols:• Link control protocol (LCP)—Establishes, tears down, and monitors data links.• Network control protocol (NCP)—Negotiates the packet format and type for data links.• Authentication protocols—Authenticate users. Protocols include the following:{ Password Authentication Protocol (PAP).{ Challenge Handshake Authentication Protocol (CHAP).{ Microsoft CHAP (MS-CHAP).{ Microsoft CHAP Version 2 (MS-CHAP-V2).PPP link establishment processFigure 72 shows the PPP link establishment process.Figure 72 PPP link establishment process1. Initially, PPP is in Link Dead phase. After the physical layer goes up, PPP enters the LinkEstablishment phase (Establish).2. In the Link Establishment phase, the LCP negotiation is performed. The LCP configurationoptions include Authentication-Protocol, Async-Control-Character-Map (ACCM),Maximum-Receive-Unit (MRU), Magic-Number, Protocol-Field-Compression (PFC),Address-and-Control-Field-Compression (ACFC), and MP.{ If the negotiation fails, LCP reports a Fail event, and PPP returns to the Dead phase.{ If the negotiation succeeds, LCP enters the Opened state and reports an Up event,indicating that the underlying layer link has been established. At this time, the PPP link is notestablished for the network layer, and network layer packets cannot be transmitted over thelink.3. If authentication is configured, the PPP link enters the Authentication phase, where PAP, CHAP,MS-CHAP, or MS-CHAP-V2 authentication is performed.{ If the client fails to pass the authentication, LCP reports a Fail event and enters the LinkTermination phase. In this phase, the link is torn down and LCP goes down.{ If the client passes the authentication, LCP reports a Success event.Dead EstablishUp AuthenticateOpenedTerminate NetworkDownFail Fail Success/NoneClosing
