Setting up Serial Line Interface Protocol (SLIP) on Linux/*BSD

Introduction

Creating a connection for uIP on a Linux or BSD box is relatively simple, although instructions are not necessarily easy to find. Before you start, it's always good to verify that your serial connection to the uIP machine is wired correctly. The easiest way to do this is simply start up terminal programs on each and see if typing on one system causes tect to appear on the other. For the Linux machine, I would suggest using Minicom (http://alioth.debian.org/projects/minicom/). For the uIP system running (presumably) MS-DOS, I would suggest BinkleyTerm 2.40 or earlier as these versions will exercise the FOSSIL driver as well.

Setting Up SLIP

To start SLIP on the Linux box, enter the following command as root:

slattach -s 9600 -p slip -L /dev/ttyS0 &

The program slattach initiates the serial connection. The option -s specifies the speed; 9600 bps is a reliable starting point for trying out your SLIP connection. The -p option specifies the protocol. Specifying slip is important because slattach normally defaults to CSLIP, compressed SLIP, which uIP does not support. The device specification is refering to the first serial port on the Linux system. Finally, the ampersand forces this program into the background, which is necessary before continuing.

At this point, you may have received some cryptic error, such as:

SLIP_set_disc(4): Invalid argument

This error means that SLIP support has not been compiled into your kernel. Your version of Linux/BSD will not support the SLIP protocol. To fix this problem, you can:

1. Install a different Linux distribution (Debian x86, for example, supports SLIP)
2. Recompile your kernel (easy for *BSD OSes, quite a task for Linux)
3. Try a different machine with a different version of Linux 4. Use a Live CD (SLAX http://slax.linux-live.org/ supports SLIP, for example)

Bringing Up the Network

To start the network over the SLIP connection, one more command is necessary. Again, as root, type:

ifconfig sl0 192.168.1.51 pointopoint 192.168.1.50 up

Note that these IP addresses refer to the defaults hard-coded into uip.h. If you recompile uIP, make sure to update these IP addresses. The first IP address is the Linux/BSD machine. The second refers to the uIP machine. The IP address of the Linux machine will only refer to the SLIP connection; your ethernet IP address on you LAN/Internet connection should be unaffected by this command.

After typing this last command, the uIP machine should be visible to the Linux/BSD box for all users!

Cleaning Up

When your're all done with your SLIP connection, it's always a good idea to bring down the SLIP network. Start by typing the command:

ifconfig sl0 down

Easy, right? Next, the slattach process must be killed. You'll need slattach's process id to do so. Once you have it, type:

kill #

It may take a few seconds, but eventually the slattach process should die. If you have a graphical desktop running, using a task manager-type program would be the easier way to kill slattach.

Problems

I can't think of any problems at this time. Please note that these instructions worked for me, but they may not work for you. Also, no guarantee concerning the correctness or safety/security of these instructions is given. Proceed at your own risk.

Other OSes

You're on your own on other OSes. This procedure will probably work on most UNIX-like operating systems (Solaris, HP-UX, etc.). It might even work on Mac OS X. On MS Windows systems, you'll need an older version that still supports standard SLIP. Windows XP and Windows 2000 do _not_ support plain old SLIP any longer to the best of my knowledge. Windows 95 and Windows 98 might, however. If you're using Windows ME, then I'd have to ask, why? If you're using MS-DOS as the router, then you're really missing the point of this uIP distribution.

Thanks

Most of these instructions have been taken from "uIP for the TRS-80 Model3" website (http://www.geocities.com/maboytim/uip/). His directions on setting up the actual SLIP connection are quite complete.

-Jeff Armstrong
January 6, 2005