Linux-Modem-Sharing(1).pdf

Modem Sharing mini−HOWTO

Friedemann Baitinger

fb@baiti.net

2001−08−22

Revision History

Revision v1.12

2001−08−22

Revised by: gjf

Corrected author's email

Revision v1.11

2001−07−12

Revised by: aeg

Converted to DocBook SGML

Revision v1.10

1999−09−11

Revised by: fb

Added "Feedback from the Users" section

Revision v1.01

1997−06−12

Revised by: fb

Converted source to HTML

Describes how to setup a Linux system to share a modem with other systems over a TCP/IP network.

Modem Sharing mini−HOWTO

Table of Contents

1. Legal Notice. ....................................................................................................................................................1

2. The Server Side. ..............................................................................................................................................2

2.1. Masqdialer Installation. .....................................................................................................................3

2.2. Masqdialer Configuration. ................................................................................................................3

3. The Client Side. ...............................................................................................................................................4

4. Security Considerations. .................................................................................................................................5

5. Examples. .........................................................................................................................................................6

6. Feedback From Users. ....................................................................................................................................7

1. Legal Notice

conditions set forth in the GNU Free Documentation License at < http://www.gnu.org/copyleft/fdl.html > .

1. Legal Notice

2. The Server Side

It is assumed that the server is a Linux system with either:

· an 'isdn4linux'−emulated modem mapped to a /dev/ttyIx device

a modem attached to a /dev/ttySx device

The easiest setup I can think of uses a five lines perl script to implement a modem daemon in

/usr/sbin/modemd :

#!/usr/bin/perl

select((select(STDOUT), $| = 1)[$[]);

select((select(STDIN), $| = 1)[$[]);

exec 'cu −s 115200 −l /dev/ttyS1';

die '$0: Cant exec cu: $!\n';

The modem daemon is started by the inetd process if a client connects to the appropriate port as described

below. The modemd simply connects the socket handle with STDIN and STDOUT of the cu command and

lets cu handle the actual modem device.

The existence of the modem daemon must be made known to the inetd process by updating its configuration

file, usually /etc/inetd.conf like:

# modem daemon

modem stream tcp nowait root /usr/sbin/tcpd /usr/sbin/modemd /dev/ttyS1

In order to make this work, an entry to /etc/services needs to be added like:

modem 2006/tcp modemd

This associates a symbolic name with an explicit port, 2006 in the example. The portnumber could be any

number not already assigned to an existing service. After these changes have been made, a signal must be

sent to the inetd process in order to let inetd re−read and process its configuration file:

bash# ps | grep inetd

194 ? S 0:00 /usr/sbin/inetd

bash# kill −HUP 194

Now the server side is ready to accept requests from clients. The correct function can be verified by:

bash$ telnet localhost modem

Trying 127.0.0.1...

Connected to localhost.

Escape character is '^]'.

You are now connected to the modem. You can now issue AT commands in order to verify the setup:

atz

2. The Server Side

Modem Sharing mini−HOWTO

atz

ati1

Linux ISDN

telnet>quit

bash$

Instead of using the Perl script as a modem server, there is also a program named Masqdialer available at

http://w3.cpwright.com/mserver/ .

With Masqdialer you can export any number of modems connected to your server to any host that can

connect the server via TCP/IP on a given port with a binary data stream.

2.1. Masqdialer Installation

Before compiling check config.h for compile time options:

· set the path for the lock file to your liking

set the path for the config file to your liking

Do make all .

Copy the binaries ( mserver and tcpconn ) into a suitable directory such as /usr/local/sbin/. Copy

mserver.conf into the path that you specified in config.h .

Masqdialer could be started from one of your system startup scripts. A simple /usr/local/sbin/mserver will

run it as a daemon.

2.2. Masqdialer Configuration

A line in mserver.conf could look like this:

5800 /dev/ttyS1 115200,8,N,1 *.foo.org,192.168.2.1

which would mean that a modem connected to /dev/ttyS1 can be connected via port 5800 from anywhere

in the domain foo.org and from host 192.168.2.1. Any other hosts are rejected. Pitfall: If you don't specify

hosts then ANY host will be allowed to connect. The serial line settings are fixed and cannot be changed from

the client side. You can export several modems on a single port. Masqdialer only locks the modem devices by

use of UUCP style lock files when they are actually in use thus allowing other programs to take advantage of

them.

2.1. Masqdialer Installation

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: