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3. Installing PPP

Linux PPP operations come in two parts: PPP support code in the kernel, and a PPP daemon. We will tackle each in turn.

3.1 Compiling PPP Support into the Kernel

Many distributions seem to provide PPP kernel support in their default installation kernels, but others do not.

If at boot your kernel reports messages like

PPP Dynamic channel allocation code copyright 1995 Caldera, Inc.
PPP line discipline registered.
then your kernel does have PPP support compiled in. You can check these boot-time messages using the command

If you do not have kernel support for PPP, you will need to re-build the kernel. See your distribution's documentation, or the Kernel-HOWTO at The Linux Kernel HOWTO for full details.

3.2 Obtaining and Installing the PPP Daemon

You will need version 2.0 or better of the PPP Daemon, pppd. You can check if pppd is installed, and find out its version number using

pppd -version
(or maybe /usr/sbin/pppd -version).

If you need to install pppd, look first on your distribution disks or web site. If your Linux distribution does not include the PPP software, you will need to obtain and compile the Linux PPP daemon source code. Locate a file named ppp-X.Y.Z.tar.gz, and choose the latest version (i.e., highest version X.Y.Z) available from this site.

The PPP package contains instructions on how to compile and install the software so this document does not!

3.3 Configuring the Chat Script

Copy the following chat script to /etc/ppp/chat/das.

'' ATZ
OK-ATZ-OK ATM0D3988211
name:--name:--name:--name: _your_das_username_here_
sword: _your_das_password_here_\q
Box "ppp /compressed default"

Edit the script:

  1. Replace the string _your_das_username_here_ with your DAS user name.
  2. Replace the string _your_das_password_here_ with the password. Note that there is a trailing '\q' after the password with no space between the password and '\q'. Leave it there: it suppresses writing the password into log files.

If you need to embed a space into either the username or the password, you can quote the string. For example: "this password has spaces". Finally, note that your DAS password is contained in cleartext in this file, so it must be protected:

chmod 600 /etc/chat/das

3.4 Testing the PPP Daemon Manually

First, make sure you are logging debug-level syslog messages. If your /etc/syslog.conf does not have a line such as:

        *.debug;cron.none       -/var/log/debug

then put one there, and make syslog re-read the file with kill -HUP `cat /var/run/`, or similar.

Next, attempt to set up a PPP connection with a command such as:

pppd ttyS1 38400 modem crtscts defaultroute lock \
        netmask \
        connect "chat -v -f /etc/ppp/chat/das"

You must, of course, replace ttyS1 with the name of the serial port to which your modem is connected. Remember, DOS COMn translates to ttySn-1 in linux.

The '-v' option for chat turns on verbose mode, in which the complete chat dialog is logged to syslog. After the above modification, debug-level syslog messages are being logged to the file /var/log/debug. You should tail -f /var/log/debug now to check the progress of the chat script.

Assuming all goes well, you will eventually see a message in the syslog similar to:

        Sep 19 12:25:27 hilbert pppd[17524]: Connect: ppp0 <--> /dev/ttyS3
        Sep 19 12:25:30 hilbert pppd[17524]: local  IP address
        Sep 19 12:25:30 hilbert pppd[17524]: remote IP address

(The IP addresses will be different, of course)

You're on the net! Running ifconfig should show a ppp0 interface. The net tools, such as telnet, should now work. Of course, there may be something amis with the nameserver at this point. So it is prudent to first try with an IP address: telnet If that works, try with the name: telnet nova.

Your PPP connection is ended by: kill -HUP `cat /var/run/ppp*.pid`. The syslog should show the link going down.

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