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There are several possibilities:
- Your LAN is an official Class C net with IP addresses valid on the Internet.
This case is the easiest of configure. You give each network card on your
network one of these addresses and set a default route on the ISDN card that
goes to your provider.
- You'd only like to do http in Internet from your LAN. In this case you
can make up IP addresses for your LAN; the only official IP address is that for
your ISDN card. Then install a proxy server on your Linux router, and enter it
in all of your browsers. In this case you do not need a default route.
- From your LAN you only want to log in to your Linux ISDN router and FROM
THERE do your work on the Internet. This is even simpler, then you don't even
need a proxy server.
- Use ip masquerading. This is the most comfortable one to use, but more
difficult to set up. The Linux computer acts as a gateway. The trick is that it
hides the ip addresses of the LAN, by giving its own internet address as
response address. When receiving the response, it will forward it to the
correct computer on the LAN. You can also use masquerading with dynamic ip
addresses. If you don't want to start the ISDN connection from the Linux
computer to your internet provider manually, then you can set up dial on demand
functionality (see section
dod).
On the Linux side use modemd, which is a very short perl script
(also see Linux Modem sharing mini-HOWTO at
http://www.linuxdoc.org/HOWTO/mini/Linux-Modem-Sharing.html
):
#!/usr/bin/perl
select((select(STDOUT), $| = 1)[$[]);
select((select(STDIN), $| = 1)[$[]);
exec "cu","-E","''", "-l", "$ARGV[0]";
die "$0: Cannot exec cu: $!\n";
It has to be started by inetd, therefore this has to be added to
/etc/services
:
modem 20006/tcp modemd # Modem service via TCP
isdn 20007/tcp modemd # ISDN service via TCP
And this has to be added to /etc/inet.conf
:
modemd stream tcp nowait root /usr/sbin/tcpd /usr/sbin/modemd ttyI5
Instead of modemd you can also use the program mserver, which has some
additional functionality (e.g. rights based on ip address):
ftp://ftp.innet.be/pub/staff/carl/
Additionally, you need some software on your non-ISDN computer which emulates a
serial port, but redirects it via telnet to the Linux ISDN computer.
Some telnet clients allow this functionality (e.g. some uucicos).
If you generally want to offer all applications a kind of "remote COM
port", then there is COMT for Windows (95), and
"telser.device" for Amigas. Disadvantage of COMT: it is only
visible to ancient 16bit Win applications, and not even working in the DOS box.
Another program is DialOut/IP, but it's fairly expensive ($70).
COMT may be found on Simtel:
http://educom.sce.fct.unl.pt/ftp/pub/shareware/win-utils/comt2.zip
DialOut/IP can be found on:
http://tacticalsoftware.com
Those who just want to save their CrossPoint installation should be aware that
it now offers tcp modem support, such that it will run without additional
software. Check out:
http://www.openxp.de
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