  call-back mini HOWTO
  by Pawel Skonecki, stona@fizyka.umcs.lublin.pl
  v1.1a, June 2000

  This document describes how to set up call-back by using the Linux
  system and modem. I would like to thank Anna for her patience.
  ______________________________________________________________________

  Table of Contents


  1. Introduction

     1.1 OPINION
     1.2 PUBLISHING

  2. Procedure

     2.1 PART I: Net at home ?
     2.2 PART II: The first steps with modem.
     2.3 PART III Call Linux
     2.4 PART IV Linux calls us
     2.5 PART V Summary


  ______________________________________________________________________

  1.  Introduction

  1.1.  OPINION

  I'll will be waiting for all opinions about this document. I have
  tried to gather information as complete as possible. Tell me when your
  find any mistakes. I'll be grateful to people who will send me any
  suggestions or corrections. Their contributions will make this
  document better.  I don't mind answering your questions but I'd rather
  you read the whole article first.


  1.2.  PUBLISHING

  This document can by published under the conditions of Linux
  Documentation Project. Get in touch with the author if you can't get
  this license.  This document is free.


  2.  Procedure

  2.1.  PART I: Net at home ?

  Most of us use the Internet in a place of work. However we offen need
  the net at home or outside the place of work. It may be possible that
  the work from home is cheaper then from a company building. I think
  that the best solution is to install call-back software on the Linux
  server. Call-back makes it possible to re-call index number at the
  cost of the company. I'll try to present how it works. An entitled
  person calls modem is varied for the first time in Linux server. Then
  on the user's side the "hang up modem" is switched on. At the same
  time Linux calls the user. User is verified again. We have connection
  and the server is charged. The user pays only for the initiation of
  connection. The double verification and extra options in the call-back
  program unable the unsuitable persons to charge our bill. We can
  restrict the access to the connection only to corporation network or
  Internet.  Call-back is very flexible. Below, I'll try to present the
  configuration of a call-back server on Linux system and I'll show you
  how to set up your computer for re-calling the connection.
  2.2.  PART II: The first steps with modem.

  The administrators prefer different modem but while buying a modem we
  should remember about certain rules:


  ·  Don't buy the Win-Modem because it doesn't work with Linux

  ·  The external modem works faster than the modem which is inside your
     computer

  ·  The internal modem with ISA slot is better then the are with PCI
     slot (you can use your PCI slot for something different)

  ·  Don't use Plug&Play modem. If you have it set off, Plug&Play
     options and set up modem on free com (read Plug&Play-HOWTO).


  When we have the suitable modem we have to set it up in our system.
  We have to check on which com our modem is. Then we have to make a
  symbolic link to this hardware and /dev/modem. For example, if we have
  the modem for the 2nd com we write:


  ln -s /dev/cua1 /dev/modem



  We check it


  lrwxrwxrwx 1 root uucp 9 Sep 19 19:10 /dev/modem -> /dev/cua1



  If we have the modem on different com we have to remember that


  /dev/cua0 is com1

  /dev/cua1 is com2

  /dev/cua2 is com3

  /dev/cua3 is com4



  For new kernels:


  /dev/ttyS0 is com1

  /dev/ttyS1 is com2

  /dev/ttyS2 is com3

  /dev/ttyS3 is com4



  Now, we check our configuration using the program minicom.



  2.3.  PART III Call Linux

  The first step to make the call-back on Linux accessible is to set up
  a suitable parameter in kernel. Then we check whether our kernel
  serves the protocol ppp. If you don't have ppp in your kernel or in
  module you will have to compile your kernel and add ppp. You will find
  more information in Kernel-HOWTO. OK. We have a good kernel.  Now, we
  have to set up software to our system. The call-back program is a part
  of mgetty-sendfax and ppp. You will find it all in your distribution.
  Because call-back system we have double verification and we create a
  user who will be running ppp on the side of server.


  pppuser:klkIOM89mn65H:230:PPP Dialin:/home/pppuser:/etc/ppp/ppplogin



  Then change the password. We have to add information abut password in
  the file /etc/ppp/pap-secrets (more in man pppd)


  pppuser * password_for_pppuser *



  This user doesn't have a usual shell but a file /etc/ppp/ppplogin.  We
  have to make it ourselves. for example vi /etc/ppp/ppplogin and we
  type:


  #!/bin/sh

  exec /usr/sbin/pppd -detach 192.168.1.1:192.168.1.2



  where the address 192.168.1.1 is the address of server with modem and
  the address 192.168.1.2 is the address which we assigned to our modem.
  We set up executable options for this file. Because we will use the
  ppp demon we have to set up the options for this demon. We edit file
  /etc/ppp/options:


  netmask 255.255.255.0

  proxyarp

  lock

  crtscts

  modem



  Proxyarp is the most important from the above options, because you can
  go to Internet by the modem in the server. The remaining options are
  used control your modem. Your user can work only in local network if
  you remove proxyarp option. You have to see PPP-HOWTO and man pppd for
  more information. We will set up our modem now. Our server must be
  ready to receive a connection after start. We edit file /etc/inittab
  and we add it's to modem on the 2en com.


  s1:2345:respawn:/sbin/mgetty ttyS1 -D /dev/ttyS1 vt100

  For the 1st com line looks as follows:


  s0:2345:respawn:/sbin/mgetty ttyS1 -D /dev/ttyS1 vt100



  We make init q. If we don't have information about any mistakes in
  logs we go to the next step. We come back to directory /etc/ppp and
  create options.ttyS1 (for modem com1 options.ttyS0)


  IP_local: IP_remote



  for our net it will be


  192.168.1.1:192.168.1.2



  We have done a lot work so far. Now, we check the file
  /etc/mgetty+sendfax/login.config. The most important line is:


  /AutoPPP/ - a_ppp /usr/sbin/pppd auth -chap +pap login detach kdebug 7 debug



  The remaining lines can be marked #.


  We have to set up suid for ppp demon, because pppuser has to run pppd
  and make interface work.


  chmod u+s /usr/sbin/pppd



  and its effect is:


  -rwsr-xr-x 1 root root 106892 Jan 11 1999 /usr/sbin/pppd



  I think that it is a good idea is to add it to cron becouse I had a
  problem after restart of my server pppd changed preference.  Our
  server will work as router. We have to enable IP forwarding and we add
  this line for the file /etc/rc.d/rc.local :


  echo "1" > /proc/sys/net/ipv4/ip_forward



  If you are RedHat user you can change in /etc/sysconfig/network from
  FORWARD_IPV4=false to FORWARD_IPV4=true.


  For verification we call to Linux. We use scripts for it. If we do
  this in MS Windows we mark options "call out a terminal after
  connection".  We login as pppuser with its password. I hope that all
  is OK.


  2.4.  PART IV Linux calls us

  We can already call our Linux. Now it's time Linux called us. It's not
  very diffucalt. We have to edit only two files. We create a file
  /etc/mgetty+sendfax/callback.conf and we leave it empty.


  Then we have to ask our users for their phone number. It's time to
  write the numbers we have connected earlier. In order to do it we edit
  /etc/mgetty+sendfax/login.conf and add line:


  call - - /usr/sbin/callback - S 123456



  where call is a pseudo-user needed to initiate the connection. The
  line in the /etc/mgetty+sendfax/login.conf puts in motion the program
  calling the given number (in this case it's 123456). The same
  procedures can be applied to other users. I'll try to explain how it
  works. When we call a server. It asks us to give verification. We
  login as pseudo-user, in this case it calls. The script in our
  computer hangs up the modem.  We wait and the connection is cut off.
  The program call-back starts working and recalls us. We verify
  ourselves again as pppuser with password. We combine the connection
  and interface ppp. That's all. The configuration of work-stations is
  very simple. When you have MS Windows, you have to install dial-up for
  your number. In the modem propriety we find "
  propriety--->extended---> extra options" where we write.


  &c0s0=1



  We close the window and call. We log in according to the description
  given above. If we want to use Linux, we must refer to the script.
  It's difficult to give only one good script for our Linux. A good
  configuration of ppp in the system is of primary importance. (You can
  call it as pppuser through the scripts first).The scripts below were
  whiten by A. Gozdz. I suggest putting everything to catalogue.  It is
  only my suggestion & you don't have to start the scripts here.
  Detailed information cocernig writing scripts on Linux can found in
  PPP-HOWTO.


  THESE SCRIPTS WORK WELL WITH SLACKWARE


  The configuration file of daemon ppp (an example for modem on com2)
  /etc/options



  lock

  defaultroute

  noipdefault

  modem

  /dev/cua1

  33600

  crtscts

  debug

  passive

  asyncmap 0



  and the specific scripts


  ·  the first named /etc/ppp/ppp-call


     #!/bin/bash

     teksta="Connection failed"

     tekstb="Probably, You will be connect"

     # /sbin/setserial /dev/cua1 spd_vhi

     killall -INT pppd 2>/dev/null

     rm -f /var/lock/LCK* /var/run/ppp*.pid

     (/usr/sbin/pppd -detach /dev/ttyS1 115200 \

     connect "/usr/sbin/chat -v -f /etc/ppp/pppcallback" &) || \

     (echo $teksta; ls marsss >/dev/null; exit 1)

     echo $tekstb

     exit 0



  ·  the second file called /etc/ppp/pppcallback



     TIMEOUT 60

     ABORT 'ERROR'

     ABORT 'BUSY'

     ABORT 'NO ANSWER'

     ABORT 'NO DIALTONE'

     ABORT '\nVOICE\r'

     ABORT '\nRINGING\r\n\r\nRINGING\r'

     ´
     TIMEOUT 75

     OK ATDT123456

     CONNECT ''

     ogin:-ogin: ppp_pseudouser


     TIMEOUT 180


     CONNECT ''

     TIMEOUT 20

     ogin:-ogin: pppuser

     sword:-sword password_for_pppuser



  ·  You can ppp-call, now. :)


  THESE SCRIPTS WORK GOOD WITH LINUX RED HAT 6.x


  ·  /etc/ppp/options


     lock

     defaultroute

     noipdefault

     modem

     33600

     crtscts

     debug

     passive

     asyncmap 0



  ·  /etc/ppp/pppcallback


     TIMEOUT 5

     ABORT 'ERROR'

     ABORT 'BUSY'

     ABORT 'NO ANSWER'

     ABORT 'NO DIALTONE'

     ABORT '\nVOICE\r'

     ABORT '\nRINGING\r\n\r\nRINGING\r'

     ´
     TIMEOUT 40

     OK ATDT5376443 CONNECT ''

     ogin:-ogin: ppp-pseudo-user


     TIMEOUT 180


     CONNECT ''

     TIMEOUT 20

     ogin:-ogin: pppuser

     sword:-sword password_for_ppuser



  ·  /usr/bin/ppp-call


     #!/bin/bash

     teksta="Connection failed"

     tekstb="Probably, You will be connect"

     # /sbin/setserial /dev/cua1 spd_vhi

     killall -INT pppd 2>/dev/null

     rm -f /var/lock/LCK* /var/run/ppp*.pid

     (/usr/sbin/pppd -detach call ppp_call &) || \

     (echo $teksta; ls marsss >/dev/null; exit 1)

     echo $tekstb

     exit 0



  ·  You can run ppp-call, now. :)


  If you have M$ Windows you can use this script for conection. I don't
  test it (I use terminal) you can ask some more Adrian Debkowski
  (adrian@cr-media.pl).


  proc main

  delay 1

  waitfor "ogin:"

  transmit "call^M"

  waitfor "RING"

  transmit "ATA^M"

  waitfor "CONNECT"

  waitfor "ogin:"

  transmit "pppuser^M"

  waitfor "word:"

  transmit "ppp^M"

  endproc



  2.5.  PART V Summary

  The Configuration of call-back is not complicated. The most important
  thing is a proper arrangement of ppp server on Linux. I don't know a
  better way of setting up an access - server. The configuration
  presented above is a result of numerous attempts and it can be done in
  a different way. That's way I suggest reading all documents concerning
  this issue man pppd, NET4-HOWTO, PPP-HOWTO.



