4000 Router Series Layer 2 - WAN Configuration Guide

Configuring PPP and MP

This feature is supported only on routers installed with SAE, AS, ASE, BS, E1, E1-F, T1, T1-F, POS, CPOS,

CE3, or AM interface modules. For more information about interface modules, see HP MSR Router Series

Interface Module Guide.

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—Authenticate users. Protocols includes Password Authentication Protocol

(PAP) and Challenge Handshake Authentication Protocol (CHAP).

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, Async-Control-Character-Map (ACCM), Maximum-Receive-Unit

(MRU), and Magic-Number. 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 or CHAP

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. If the NCP negotiation succeeds, the link goes up and

Dead Establish

Authenticate

Opened

Terminate Network

Down

Fail Fail

Success

/None

Closing