LPI Linux Certification in a Nutshell, 2nd Edition

Objective 4: Configure Linux as a PPP Client

The Point-to-Point Protocol (PPP) is a method of constructing a network connection between two systems using a serial interface. Usually, this interface is a pair of modems connected by a telephone call over a switched voice network. However, PPP isn't specifically tied to the use of modems and can also work with a direct serial connection using a null modem cable (sometimes known as a crossover cable. When PPP is implemented on a Linux system, it creates a new network interface, usually ppp0, which is configured for use with TCP/IP and an IP address.

To use PPP, your kernel must be compiled with PPP support . Most distributions include PPP support in the kernels they install, but if yours doesn't or if you build your own kernels, you must select PPP Support under Network Device Support in your kernel configuration (see Chapter 13 for information on compiling kernels).

Clients and Servers

PPP is a peer-to-peer protocol, in which there is no technical difference between the two systems sharing a PPP link. When used for dial-up communications, however, it is convenient to think of the system making the call as a PPP client and the system being called as a PPP server. Linux can do both jobs simultaneously if multiple serial interfaces are available, but this section covers only the client-side configuration as required by Exam 102.

Serial ports and modems

The only hardware required to create a PPP dial-up connection is a serial interface ...