SERIAL-IP(8)

NAME
serial-ip - Serial IP (SLIP or PPP) setup

DESCRIPTION
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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...
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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 example above.

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 like:

[telnet] | /dev/tcp0 | inet | [ethernet] | inet | /dev/tcp0 | [in.telnetd]

One-half (!) of a SLIP connection would look like this:

[telnet] | /dev/tcp2 | inet | /dev/psip2 | slip | [serial line] ...

  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 this:

    # 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 configured networks.)

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):

    netdefault psip2

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 list. 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)
XXX

  Configuration for a SLIP - Ethernet router (complex case)
XXX

FILES

/dev/psip*
    Pseudo-IP devices for use by slip and ppp.

SEE ALSO
boot(8), inet(8), netdefault(8), term(1), chat(1).

BUGS

AUTHOR
Kees J. Bot (kjb@cs.vu.nl)