Linux Networking/PLIP for Linux-2.0

PLIP for Linux-2.0

PLIP device names are `plip0', `plip1 and plip2.

Kernel Compile Options:

             Network device support  --->
                 <*> PLIP (parallel port) support

plip (Parallel Line IP), is like SLIP, in that it is used for providing a point to point network connection between two machines, except that it is designed to use the parallel printer ports on your machine instead of the serial ports (a cabling diagram in included in the cabling diagram section later in this document). Because it is possible to transfer more than one bit at a time with a parallel port, it is possible to attain higher speeds with the plip interface than with a standard serial device. In addition, even the simplest of parallel ports, printer ports, can be used in lieu of you having to purchase comparatively expensive 16550AFN UART's for your serial ports. PLIP uses a lot of CPU compared to a serial link and is most certainly not a good option if you can obtain some cheap ethernet cards, but it will work when nothing else is available and will work quite well. You should expect a data transfer rate of about 20 kilobytes per second when a link is running well.

The PLIP device drivers competes with the parallel device driver for the parallel port hardware. If you wish to use both drivers then you should compile them both as modules to ensure that you are able to select which port you want to use for PLIP and which ports you want for the printer driver. Refer to the ``Mudules mini-HOWTO for more information on kernel module configuration.

Please note that some laptops use chipsets that will not work with PLIP because they do not allow some combinations of signals that PLIP relies on, that printers don't use.

The Linux plip interface is compatible with the Crynwyr Packet Driver PLIP and this will mean that you can connect your Linux machine to a DOS machine running any other sort of tcp/ip software via plip.

In the 2.0.* series kernel the plip devices are mapped to i/o port and IRQ as follows:

        device  i/o     IRQ
        ------  -----   ---
        plip0   0x3bc   5
        plip1   0x378   7
        plip2   0x278   2

If your parallel ports don't match any of the above combinations then you can change the IRQ of a port using the ifconfig command using the `irq' parameter (be sure to enable IRQ's on your printer ports in your ROM BIOS if it supports this option). As an alternative, you can specify ``io= annd ``irq= options on the insmod command line, if you use modules. For example:

            root# insmod plip.o io=0x288 irq=5

PLIP operation is controlled by two timeouts, whose default values are probably ok in most cases. You will probably need to increase them if you have an especially slow computer, in which case the timers to increase are actually on the other computer. A program called plipconfig exists that allows you to change these timer settings without recompiling your kernel. It is supplied with many Linux distributions.

To configure a plip interface, you will need to invoke the following commands (or add them to your initialization scripts):

            root# /sbin/ifconfig plip1 localplip pointopoint remoteplip
            root# /sbin/route add remoteplip plip1

Here, the port being used is the one at I/O address 0x378; localplip amd remoteplip are the names or IP addresses used over the PLIP cable. I personally keep them in my /etc/hosts database:

            # plip entries
            192.168.3.1   localplip
            192.168.3.2   remoteplip

The pointopoint parameter has the same meaning as for SLIP, in that it specifies the address of the machine at the other end of the link. In almost all respects you can treat a plip interface as though it were a SLIP interface, except that neither dip nor slattach need be, nor can be, used.

Further information on PLIP may be obtained from the ``PLIP mini- HOWTO.