"Linux Gazette...making Linux just a little more fun!"

The Answer Guy

By James T. Dennis, [email protected]
Starshine Technical Services, http://www.starshine.org/

Connecting Linux to Win '95 via Null Modem

From Chris Gushue on 04 Jun 1998

I have two systems, a 486 and a K6, and I was wondering how (if) I could connect them using a serial (null modem) cable. One system will be running Windows 98, the other running Linux. I can't seem to find any info on the LDP or other webpages. Thanks.

Certainly you can connect them for some purposes.

I don't know anything about Win '98 but I presume it comes with some sort of terminal emulation package (like the Hyperterm that MS licensed from Hilgreave for Win '95, or that cheesy old "Terminal" that they used to ship with Windows 3.x).

You could also get any of several shareware, free, or commercial communications packages such as Telix (Windows or DOS), Kermit (DOS) or K95 (Windows), etc.

All of these should have a "direct" or "null modem" option listed among their "connection/modem" types.

This will give you a basic, character modem terminal login to your Linux box. This not a networking connection --- it is just like connecting a dumb terminal to the machine (which still gives you access to most of the applications and almost all of the utilities and programming tools on your Linux system).

If you want networking between these two systems, over the serial line; that's a different story. You should be able to establish a SLIP or PPP connection between the two. Once you've done that you could run any of the TCP/IP protocols over the line. However, it's much trickier to do that --- and I have no idea how Win '98 will handle it.

(Under early revisions of Win '95 I remember complaints that the supplied PPP drivers and their user interface was configured to work with MSN (Microsoft Network --- their ISP) and that it required some utility from the "Plus Pack" to allow one to create and maintain a "chat" script --- a way to log in and configure/establish a PPP session with any other ISP.

It seems that MS also added features in their NT 4.x (RAS?, RRAS?) that allow these systems to act as recipients of the stock Win '95 MS-CHAP authentication method. I guess this was a bid to convince ISP's to adopt Windows NT for their work.

Meanwhile Gert Doering (and others?) released the AutoPPP extensions or patches to 'mgetty.'

'mgetty' is Gert's very popular "modem getty" line that allows a modem line to be shared between terminal, fax, network and even voice (with some modems) for both incoming and outgoing use. One of the features of 'mgetty' is that it can be configured to recognize certain login strings ("user name patterns") as a directive to use an alternative 'login' program.

Thus you can configure you modem line to use ppplogin when given a "user" name of the form: Pmaryjoe, and to use a traditional 'login' when presented with others.

I personally haven't set up AutoPPP. However, a quick Yahoo! search on the string: "+mgetty +autoppp" gives about 450 Alta Vista hits. Most of these are from the Linux ISP mailing list. I didn't spot any that covered AutoPPP over a null modem.

Trying a search string like: + "null modem" +mgetty +win + "95"

... didn't help either. Though it did return a bunch of links to Linux Gazett mirror sites carrying issues 18, 25, and 28 (false hits in this case)

Somewhere on the Linux ISP mailing list archives I found a thread about "null serial" that was on target but not very informative. Someone mentioned that the Win '95 PPP couldn't handle direct connection --- and suggested Trumpet Winsock (a third party TCP/IP suite for Windows --- and DOS --- for years before MS had ever heard of TCP/IP).

So, it may not be easy to get networking configured over a null modem line so long as Win '9x is on one end of it. However, I bet it would be possible. You should probabl create a "modem emulation" driver for Linux that would allow the Win '9x box to work as though it were sending AT commands to a modem. The "modem emulation" driver could implement a small AT command subset (responding to every valid <pause>+++<pause>AT sequence with "OK" or the appropriate response).

In the long run it's probably far easier to buy a couple of ethernet cards (less than $30 each) and a 10baseT "cross over" cable (necessary if you're not going through a hub, and sometimes necessary to cascade one hub off of another). Not only is ethernet much faster than serial --- it is currently much easier to configure and support (for networking). Another advantage is that you can later expand; buy a 4, 5 or 8 port ethernet hub and you can wire up the whole house (actually I've almost filled two 8 port hubs here --- but I'm a little different).

Conclusion: You can easily use the serial/null modem for simple terminal access. You might be able to get it working as a networking interface, but you might have quite a bit of trouble convincing Win '9x to do PPP over a "direct" or "null modem" connection. So you might have to look for a third party PPP replacement (which may need to be upgraded between the Win '95 and Win '98 versions) --- or you might be able to write some weird "modem emulation" on the Linux side. For networking it will be much easier to buy a couple of ethernet cards.

Linux help

From Chris Gushue on 04 Jun 1998

Thanks a lot for your thorough and quick response! It was just what I was looking for, just a basic login to my Linux box to play around with it until I get around to buying a hub and network cards. It kind of funny though, using my K6/233 Win98 machine as a dumb terminal to my 486/100 Linux box

I was using that VAResearch machine that I reviewed for the Linux Journal ("betelgeuse": a 266Mhz PII with 64Mb of RAM and a 4Mb Matrox Millenium video) as a dumb terminal to my old 33Mhz 386 ("antares") for months. The old 386 was where all my mail and news was. It's still the network hub, mail and news server for the house (though now I use 'fetchmail' everything over to "canopus" a home built P166; the wife mostly took over the PII).

The 386 is the most stable machine in the house -- it's the only one on a UPS.

Copyright © 1998, James T. Dennis
Published in Linux Gazette Issue 30 July 1998

	SCOkeys	chroot	dosemu-db	NTauth	cdr	3270	comport
	lilostop	emulate	ppadrivers	database	vacation	nullmodem	lockups
	gzipC	newlook	c500	solprint	vc1shell	memleak	tvcard