19.15 Parallel Line IP (PLIP)

19.15.1 Creating a Parallel Cable

You can purchase a parallel cable at most computer supply stores. If you cannot do that, or you just want to know how it is done, the following table shows how to make one out of a normal parallel printer cable.

19.15.2 Setting Up PLIP

First, you have to get a laplink cable. Then, confirm that both computers have a kernel with lpt(4) driver support:

# grep lp /var/run/dmesg.boot
lpt0: <Printer> on ppbus0
lpt0: Interrupt-driven port

The parallel port must be an interrupt driven port. You should have a line similar to the following in your kernel configuration file:

device ppc0 at isa? irq 7

Then check if the kernel configuration file has a device plip line or if the plip.ko kernel module is loaded. In both cases the parallel networking interface should appear when you directly use the ifconfig(8) command.

# ifconfig lp0
lp0: flags=8810<POINTOPOINT,SIMPLEX,MULTICAST> mtu 1500

Plug in the laplink cable into the parallel interface on both computers.

Configure the network interface parameters on both sites as root. For example, if you want connect the host host1 with host2:

                 host1 <-----> host2
IP Address    10.0.0.1      10.0.0.2

Configure the interface on host1 by doing:

# ifconfig lp0 10.0.0.1 10.0.0.2

Configure the interface on host2 by doing:

# ifconfig lp0 10.0.0.2 10.0.0.1

You now should have a working connection. Please read the manual pages lp(4) and lpt(4) for more details.

You should also add both hosts to /etc/hosts:

127.0.0.1               localhost.my.domain localhost
10.0.0.1                host1.my.domain host1
10.0.0.2                host2.my.domain

To confirm the connection works, go to each host and ping the other. For example, on host1:

# ifconfig lp0
lp0: flags=8851<UP,POINTOPOINT,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        inet 10.0.0.1 --> 10.0.0.2 netmask 0xff000000
# netstat -r
Routing tables

Internet:
Destination        Gateway          Flags     Refs     Use      Netif Expire
host2              host1              UH          0       0       lp0
# ping -c 4 host2
PING host2 (10.0.0.2): 56 data bytes
64 bytes from 10.0.0.2: icmp_seq=0 ttl=255 time=2.774 ms
64 bytes from 10.0.0.2: icmp_seq=1 ttl=255 time=2.530 ms
64 bytes from 10.0.0.2: icmp_seq=2 ttl=255 time=2.556 ms
64 bytes from 10.0.0.2: icmp_seq=3 ttl=255 time=2.714 ms

--- host2 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max/stddev = 2.530/2.643/2.774/0.103 ms