serial-ip - Serial IP (SLIP or PPP) setup
Note: This text and the serial IP code is not finished. Code needs to be
added to nonamed to allow it to be used both with and without a
connection to the Internet, and by now there is a PPP program for
standard Minix "out there" that will change everything that is said in
this text. So much to do, so little time...
This manual page describes the Minix network setup to use serial line IP.
The serial IP protocol used can either be the older SLIP by means of the
slip(8) program, or PPP (Point-to-Point Protocol), the newer and better
serial IP protocol implemented by the ppp(8) program. Alas standard
Minix only supports SLIP.
In the following text all descriptions and examples will name SLIP or the
slip program, but one may just as well read PPP or ppp. Where necessary
the differences will be noted.
A typical use of the slip program is like this:
slip /dev/psip2 </dev/tty01 >/dev/tty01
The argument of the program, the /dev/psip2 device, is one of the so-
called "Pseudo IP" devices that the Minix TCP/IP driver inet(8) offers to
implement a virtual network on. On an ethernet IP packets are received
or transmitted by the ethernet card, but packets on a pseudo IP network
are channeled back to or received from a program running in user space,
such as slip. Standard input and output are used by slip to exchange
packets with another SLIP implementation. This is normally through an
RS-232 serial line like the second serial line /dev/tty01 as used in the
If we look at the flow of data over normal ethernet then this is what a
TCP connection between two Minix machines, telnet for instance, looks
One-half (!) of a SLIP connection would look like this:
Configuration for a SLIP network only
It is important to know that as far as inet is concerned the pseudo IP
network is just another network, nothing special. So you have to
convince inet that it has to send packets out over that network. One
does this by setting a default route that makes inet believe that there
is a router somewhere on the pseudo-IP network.
Assume your machine has been given the IP address 192.168.0.13 by your
service provider. Let's choose another address on that network,
192.168.0.1 for instance. (You can use the address of the SLIP gateway
if you want to make it look pretty, but it doesn't really matter,
anything "out there" is ok.) To make Minix aware of the situation you
have to configure the pseudo IP network. For Minix-vmd you need to look
for the if-then-else-fi code in /usr/etc/rc that tests if /etc/rc.net
should be run. Copy the lines in the else clause that starts network
daemons to /etc/rc.net and add the following lines to make it look like
# My SLIP interface address.
ifconfig -h 192.168.0.13 -n 255.255.255.0
# Standard network daemons.
daemonize rarpd $named irdpd rip inetd
# Default route to the outside world.
add_route -g 192.168.0.1
For standard Minix one has to edit /etc/rc instead at the point of the
XXX comments. The ifconfig goes at the first XXX, the add_route at the
second XXX. The result is conceptually the same as the example above.
The important thing is the order: Configuration, Daemons, Routes. (First
give addresses to the networks, let the daemons meditate over the results
and possibly configure more networks (rarpd), then add routes to the
Just one thing left to do. The system uses the first ethernet network
(eth0, ip0, tcp0, and udp0) as the default network. With the program
netdefault(8) you have to change the links to the default devices
(eth/psip, ip, tcp, and udp) to point to the first pseudo IP network
(psip2, ip2, tcp2, and udp2):
In /etc/hosts list at least localhost and the name of your machine with
its SLIP address. This way your machine will boot and know its own name.
Now you need to find a way to let your system know the addresses of other
machines. There are three ways:
List the names and addresses of any other machine you wish to talk
to in /etc/hosts. Drawback: This will quickly become a pretty long
Create an /etc/resolv.conf that lists a nameserver at your ISP and
127.0.0.1 (localhost). Drawback: With the SLIP link down it takes
5 to 10 seconds for a name lookup to time out on the remote name
server before the local name server is tried.
Install the above /etc/resolv.conf when slip is started, and remove
it when slip exits. Drawback: Long running programs only read
/etc/resolv.conf at startup, so they don't notice it changing.
Run a real Internet name daemon from the named package. Drawback:
Nontrivial to set up.
Configuration for a SLIP - Ethernet router (simple case)
Configuration for a SLIP - Ethernet router (complex case)
/dev/psip* Pseudo-IP devices for use by slip and ppp.
boot(8), inet(8), netdefault(8), term(1), chat(1).
Kees J. Bot (firstname.lastname@example.org)