H3C Technologies H3C SecPath F5020 - Manual (Page 9)

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Configuring PPP
Overview
Point-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 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—Authenticates users. Protocols include Password Authentication Protocol
(PAP), Challenge Handshake Authentication Protocol (CHAP), Microsoft CHAP (MS-CHAP), and
Microsoft CHAP Version 2 (MS-CHAP-V2).
PPP link establishment process
Figure 1 shows the PPP link establishment process.
Figure 1 PPP link establishment process
1. Initially, PPP is in Link Dead phase. After the physical layer goes up, PPP enters the Link
Establishment phase (Establish).
2. In the Link Establishment phase, the LCP negotiation is performed. The LCP configuration options
include Authentication-Protocol, Maximum-Receive-Unit (MRU), Magic-Number,
Protocol-Field-Compression (PFC), and Address-and-Control-Field-Compression (ACFC). 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 not established for the network layer,
and network layer packets cannot be transmitted over the link.)
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 Link Termination phase, where the link is torn down and LCP
goes down. If the client passes the authentication, LCP reports a Success event.
4. If a network layer protocol is configured, the PPP link enters the Network-Layer Protocol phase for
NCP negotiation, such as IPCP negotiation and IPv6CP negotiation. If the NCP negotiation
succeeds, the link goes up and becomes ready to carry negotiated network-layer protocol packets.
If the NCP negotiation fails, NCP reports a Down event and enters the Link Termination phase.
Dead Establish
Up
Authenticate
Opened
Terminate Network
Down
Fail Fail Success
/None
Closing