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-Modem Sharing mini-HOWTO
-!!!Modem Sharing mini-HOWTO
-!Friedemann Baitinger
-
- fb@baiti.net
-
-
-
-
-2001-08-22
-
-
-__Revision History__Revision v1.122001-08-22Revised by: gjfCorrected author's emailRevision v1.112001-07-12Revised by: aegConverted to !DocBook SGMLRevision v1.101999-09-11Revised by: fbAdded "Feedback from the Users" sectionRevision v1.011997-06-12Revised by: fbConverted source to HTML
-
-
-
-
-
-Describes how to setup a Linux system to share a modem with other systems over a TCP/IP network.
-
-
-
-
-
-----; __Table of Contents__; 1. Legal Notice; 2. The Server Side: ; 2.1. Masqdialer Installation; 2.2. Masqdialer Configuration; 3. The Client Side; 4. Security Considerations; 5. Examples; 6. Feedback From Users
-!!!1. Legal Notice
-
- Copyright © 1997 Friedemann Baitinger. This document may be
-distributed only subject to the terms and conditions set forth in
-the GNU Free Documentation License at
-` http://www.gnu.org/copyleft/fdl.htmlb.
-
-
-b
-----
-!!!2. The Server Side
-
-It is assumed that the server is a Linux system with either:
-
-
-
-
-
-
-*
-
-a modem attached to a /dev/ttySx device
-
-
-*
-*
-
-an 'isdn4linux'-emulated modem mapped to a /dev/ttyIx 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 '$: Cant exec cu: $!\n';
-
-The modem daemon is started by the __inetd__ process
-if a client connects to the appropriate port as described below. The
-__modemd__ simply connects the socket handle with STDIN
-and STDOUT of the __cu__ command and lets
-__cu__ handle the actual modem device.
-
-
-
-The existence of the modem daemon must be made known to the
-__inetd__ process by updating its configuration file,
-usually /etc/inetd.conf like:
-
-
-#
-# modem daemon
-#
-modem stream tcp nowait root /usr/sbin/tcpd /usr/sbin/modemd /dev/ttyS1
-
-In order to make this work, an entry to
-/etc/services needs to be added like:
-
-
-
-modem 2006/tcp modemd
-
-This associates a symbolic name with an explicit port, 2006 in the
-example. The portnumber could be any number not already assigned to an
-existing service. After these changes have been made, a signal must be
-sent to the inetd process in order to let __inetd__
-re-read and process its configuration file:
-
-
-
-bash# ps | grep inetd
-194 ? S :00 /usr/sbin/inetd
-bash# kill -HUP 194
-
-Now the server side is ready to accept requests from clients. The
-correct function can be verified by:
-
-
-bash$ telnet localhost modem
-Trying 127...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
-atz
-OK
-ati1
-ati1
-Linux ISDN
-OK
-^]
-telnetbquit
-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 config file to your liking
-
-
-*
-*
-
-set the path for the lock 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.
-
-----
-!!!3. The Client Side
-
-At this time, only Windows client setups are described
here. On the
-client PC, a COM-port redirector for TCP/IP is required. The best
-program for this purpose I have found is
-!DialOut/IP from Tactical Software for
-Windows 3.1 and
-Windows 95. (The Windows
-3.1 version can be used under Windows
-NT for 16-bit applications only. A 32-bit
-version for Windows NT is due late summer
-1997.)
-
-
-
-!DialOut/IP presents the shared modem on
-a new virtual COM port that it adds to Windows.
-This virtual COM port can be used by Windows
-programs as if the shared modem is directly connected. Most client
-applications (including Windows 95 dial-up
-networking) accept this and work as if there were a real COM port and
-modem, with the general exception being fax applications or any others
-that need access to UART control lines. !DialOut/IP
-can be configured to provide telnet protocol processing, but that
-feature applies to certain modem pool products and not to the
-Linux setup described in this file. Note
-that, despite its name, !DialOut/IP
-can be used also by applications that wait for incoming calls.
-
-
-
-On http://www.tactical-sw.com/
-there is a page for downloading a fully functional evaluation
-version that times out in 1-2 weeks. Installation and configuration
-is handled by a setup program, with installation details in the
-README.TXT file. When you run
-!DialOut/IP, you enter the IP address
-and port number of the shared modem.
-
-
-
-!DialOut/IP is a commercial product that
-is licensed on a per-modem basis, that is, the price depends on the number
-of modems that you are sharing. The license states that you can install
-the software on any number of PC's that access the shared modems.
-
-----
-!!!4. Security Considerations
-
-If you have only one modem for all your hosts in your local area
-network, there is probably no reason to worry about security here.
-However, if any one or more of the hosts in your LAN are connected to
-the Internet by other means than using the modem we have just setup as
-a modem server, then security considerations are required, otherwise
-anybody can do a __telnet your_host modem__ and dial
-out long distance or even international calls at will.
-
-
-
-I suggest to install and configure tcp-wrappers in order to protect
-the modem server against unauthorized access.
-
-----
-!!!5. Examples
-
-I am using the setup as described in
-The Server Side and
-The Client Side to run
-Quicken on
-my Windows 95 !ThinkPad
-and do home banking with the modem attached to my
-Linux machine. The "modem" in my case is not
-even a real modem, it is an emulated modem on an ISDN-So card.
-Quicken just sees a COM port, it
-doesn't know that the device attached to the COM port is actually at
-the other end of my Ethernet LAN, nor does it know that it is not a
-standard analog modem but an ISDN device which happens to understand
-__AT__ commands.
-
-----
-!!!6. Feedback From Users
-
-Since the first release of this document in June 1997
-I have received many email messages related to the subject. In most of
-the messages people were seeking more help to get the modem sharing
-configured and running.
-
-
-
-Recently I received an interesting feedback from
-Karsten.Hilbert@gmx.net. Karsten pointed out that
-although !DialOut/IP may be a good client
-program he'd like to have a
-GPL'ed client. Karsten mentioned
-the Software Bazaar
-`http://visar.csustan.edu/bazaar/b
-and he volunteered to put in an offer. Here is what Karsen wrote:
-
-
- Date: Fri, 27 Aug 1999 17:46:39 +0200 (CEST)
-From: Karsten Hilbert `med94ecz@studserv.uni-leipzig.deb
-Reply-To: Karsten Hilbert `Karsten.Hilbert@gmx.netb
-To: fb@baiti.net
-Subject: Windows-Modemsharing-Howto
-Hi !
-The howto mentions !DialOut/IP as a good tool to connect Windows
-clients to a linux server sharing a modem.
-I agree. However, it would be more attractive to have a free,
-GPL'ed client, wouldn't it ? This I thought and decided to offer
-some money for the implementation of such a client on the
-Software Bazaar. If someone grabs the project I will pay him a
-certain amount of money if it is completed and functional. After
-that the client would be GPL'ed.
-Now, I can only offer so much money :) But other people could
-join in and offer some, too, thus increasing the incentive.
-Wouldn't your howto be a perfect place to mention this
-possibility ?
-The Bazaar can be found at:
-http://visar.csustan.edu/bazaar/
-Thought I could mention this to you.
-Karsten
+Describe
[HowToLinuxModemSharing
] here.
