Linux Network Administrator's Guide, Second Edition

More Advanced PPP Configurations

While configuring PPP to dial in to a network like the Internet is the most common application, there are those of you who have more advanced requirements. In this section we’ll talk about a few of the more advanced configurations possible with PPP under Linux.

PPP Server

Running pppd as a server is just a matter of configuring a serial tty device to invoke pppd with appropriate options when an incoming data call has been received. One way to do this is to create a special account, say ppp, and give it a script or program as a login shell that invokes pppd with these options. Alternatively, if you intend to support PAP or CHAP authentication, you can use the mgetty program to support your modem and exploit its “/AutoPPP/” feature.

To build a server using the login method, you add a line similar to the following to your /etc/passwd file:^[58]

ppp:x:500:200:Public PPP Account:/tmp:/etc/ppp/ppplogin

If your system supports shadow passwords, you also need to add an entry to the /etc/shadow file:

ppp:!:10913:0:99999:7:::

Of course, the UID and GID you use depends on which user you wish to own the connection, and how you’ve created it. You also have to set the password for the mentioned account using the passwd command.

The ppplogin script might look like this:

#!/bin/sh
# ppplogin - script to fire up pppd on login
mesg n
stty -echo
exec pppd -detach silent modem crtscts

The mesg command disables other users from writing to the tty by using, for instance, ...