How To Setup PPP for ISP Dial-Up Under Linux

This document covers my experience configuring a Toshiba Satellite Pro 400CS laptop computer running RedHat Linux version 6.0. Other systems and linux versions may require different procedures than those described here. Any multi-user system would probably need to install things differently and worry about some security issues that I don't care about since I am the only user, usually logged in as root.

My system is primarily used for web application development. I normally am NOT connected to the internet and need to test html pages and scripts which access my internet domain name within this disconnected environment. I run the Apache http server on the laptop and access my domain, www.proliberty.com, at the localhost IP address: 127.0.0.1. Obviously, the static IP addressof my domain, on the internet, is different from localhost, so when I connect to the internet and want to access www.proliberty.com, my hosts file configuration must change.

My needs were very simple and require no fancy gateways, firewalls or other connectivity issues. I do not understand DNS administration well and have only learned enough to manage to do what I need. I simply require switching between two distinct states:

1. PPP-DOWN. I am DISCONNECTED from the internet. Connected to a local network of computers using bogus IP numbers, none of which is connected to the internet.
2. PPP-UP. I am CONNECTED to the internet via serial PPP link, at which time no other computers are connected to my laptop.

PPP Operation

My System Configuration and Files For PPP

General Instructions On How To Get PPP Working

Hardware: line (modem) speed = <your modem speed>; modem port = /dev/modem

Communication: init string = ATZ; modem dial dial command = ATDT<your ISP dial-up phone number>; other script items for loggin on (send/expect).... (see man pppd or man chat for details on connect scripts)

Quit linuxconf; when prompted, choose 'activate changes'

chmod 755 /usr/sbin/pppup

chmod 755 /usr/sbin/pppdown

---

/etc/hosts.pppdown

---

/etc/hosts.pppup

127.0.0.1       localhost

---

/etc/resolv.conf.pppdown

domain proliberty.com
search proliberty.com

# I don't run any nameservers locally when not connected to the internet

---

/etc/resolv.conf.pppup

domain proliberty.com
search proliberty.com

# Substitute the nameservers you use; these are from oro.net :
nameserver 198.68.62.2
nameserver 198.68.62.42

---

/usr/sbin/pppup

# /usr/sbin/pppup

# Edit these values for your own case in the chat command, below:

# <USERNAME > replace with your username
# <PASSWORD> replace with   your password
# <MODEM_SPEED> replace with  your modem speed
# <ISP_DIALUP> replace with your isp dial-up number

# WARNING - if you have multiple users on your system, it is probably not a good idea to put
# username and password in this file if it is readable by others!

# copy config file templates needed for pppup state:

cp -f /etc/hosts.pppup /etc/hosts
cp -f /etc/resolv.conf.pppup /etc/resolv.conf

# start the PPP process and dialup your ISP
# your ISP's login procedure may be different from this.
pppd connect 'chat -v "" ATDT <ISP_DIALUP> CONNECT "" ogin: <USERNAME >  word: <PASSWORD>' \
      /dev/modem <MODEM_SPEED> noipdefault debug crtscts modem defaultroute

---

/usr/sbin/pppdown

#!/bin/sh

#/usr/sbin/pppdown

# by Ian Goldberg <iang@cs.berkeley.edu>
# modified by Greg Keraunen <gk@proliberty.com>

# restore config files to pppdown state:

cp -f /etc/hosts.pppdown /etc/hosts
cp -f /etc/resolv.conf.pppdown /etc/resolv.conf

######################################################################
#
# Determine the device to be terminated.
#
if [ "$1" = "" ]; then
        DEVICE=ppp0
else
        DEVICE=$1
fi

######################################################################
#
# If the ppp0 pid file is present then the program is running. Stop it.
if [ -r /var/run/$DEVICE.pid ]; then
        kill -INT `cat /var/run/$DEVICE.pid`
#
# If the kill did not work then there is no process running for this
# pid. It may also mean that the lock file will be left. You may wish
# to delete the lock file at the same time.
        if [ ! "$?" = "0" ]; then
                rm -f /var/run/$DEVICE.pid
                echo "ERROR: Removed stale pid file"
                exit 1
        fi
#
# Success. Let pppd clean up its own junk.
        echo "PPP link to $DEVICE terminated."
        exit 0
fi
#
# The ppp process is not running for ppp0
echo "ERROR: PPP link is not active on $DEVICE"
exit 1

Reference Documents