Call-back(1)

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call−back mini HOWTO
call−back mini HOWTO
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call−back mini HOWTO
by Pawel Skonecki,
v2.1a, 2001−10−06
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.
1.
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1.1 OPINION
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2.
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1.
1.1 OPINION
I 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.
call−back mini HOWTO
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        call−back mini HOWTO
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 who calls the 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 the 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 the 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. I don't describe configuration of ISDN call−back because I don't use ISDN in my connection to
the Internet. If you set call−back on ISDN send me your configuration. I had some problem when I changed
my kernel from 2.2.x to 2.4.x. I will describe new option for a new kernel. Remember that if you change your
kernel for high version you will have to change pppd, too. I don't create a new section for description of new
possibility in kernels 2.4.x but I write a new configurations in old section. I would like to apologise to people
who asked me about options for new kernels. I didn't have time to write a new version of HOW−TO. I have
changed my job and place of liveing. Sorry.
2.2 PART II: The first steps with modem.
The administrators prefer different modem but while buying a modem we should remember certain
guidelines:
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The externale modem is moust flexible you have more place inste your computer.
If you have USR WinModems see Linmodem−HOWTO.
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The internal modem with ISA slot is better then the are with PCI slot (you can use your PCI slot for
something different )
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Don't use Plug modem see Plag−and−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
2.1 PART I: Net at home ?
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  call−back mini HOWTO
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 parameters 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.In the kernels
2.4.x series you have to mark follow options:
CONFIG_PPP=m # CONFIG_PPP_MULTILINK is not set CONFIG_PPP_ASYNC=m
CONFIG_PPP_SYNC_TTY=m CONFIG_PPP_DEFLATE=m CONFIG_PPP_BSDCOMP=m
After compilation you have to add some lines for /etc/modules.conf
alias /dev/ppp ppp_generic alias char−major−108 ppp_generic alias tty−ldisc−3 ppp_async alias tty−ldisc−14
ppp_synctty alias ppp−compress−21 bsd_comp alias ppp−compress−24 ppp_deflate alias ppp−compress−26
ppp_deflate
You can't forget that you need new pppd demon for kernels 2.4.x (for me it was ppp−2.4.0 this ppp has some
mistake you have to get latest from ftp.samba.org in /pub/ppp ).
OK. We have a good kernel. Now, we have to set up the 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 the call−back system has
double verification we create a user who will be running ppp on the side of server. In /etc/passwd you have
new user and you have to change their shall.
pppuser:klkIOM89mn65H:230:PPP Dialin:/home/pppuser:/etc/ppp/ppplogin
I changed the above line for kernel 2.4.x this line in /etc/passwd (I use shadow and you don't see password)
pppuser:x:6778:44:PPP Dialin:/etc/ppp/:/usr/sbin/pppd
I don't use a special script for the running of pppd but I run it directly while login pppuser.
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 *
In the 2.4.x kernels you have to write in
/etc/ppp/pap−secrets
* * "" *
2.3 PART III Call Linux
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