call-back mini HOWTO
 by Pawel Skonecki, [email protected]
 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
 ([email protected]).


 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.

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