PLIP lets us run TCP/IP between parallel ports. It is useful on machines without network cards, or to install on laptops. In this section, we will discuss:
Creating a parallel (laplink) cable.
Connecting two computers with PLIP.
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.
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 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
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