PPP Overview

Point-to-Point Protocol (PPP) encapsulates Network layer information for transmission over point-to-point links. It was designed by developers on the Internet and is described by a series of documents called Request for Comments (RFCs) ”namely, 1661, 1331, and 2153. Figure 10.2 shows how PPP's layered architecture relates to the Open Systems Interconnection (OSI) model.

Figure 10.2. The OSI reference model and PPP.

PPP consists of two main components :

• Link Control Protocol (LCP) ” Establishes, configures, and tests the connection

• Network Control Program (NCP) ” Configures many different Network layer protocols

Configuring PPP

Configuring PPP on a Cisco router requires that both global and interface configuration commands be executed on both the local and remote routers. Figure 10.3 presents an example of two routers that need to establish a PPP link.

Figure 10.3. Point-to-Point Protocol (PPP).

A username and password must be set, so the following global configuration command must be executed:

 Username  name  password  secret-password  

In this command, name and secret-password indicate the name of the remote host and the password to use for authentication. The password must be the same on both the local and remote routers. Table 10.3 lists the interface commands that must be executed to configure PPP. Figure 10.4 presents the global and interface configuration commands for router A and router B.

Figure 10.4. PPP configuration.