Note computer A and computer B are identical. They both
have bidirectional parallel ports correctly configured, as
shown below.

1). Kernel 2.2.12-20 i386
2). Stock out of the box RH 6.1 install
3). parport module loaded
4). parport_pc io=0x378 irq=7 dma=7 loaded
5). plip parport=0 module loaded
6). computer A-ifconfig plip0 192.168.1.1 pointopoint 192.168.1.2
7). computer B-ifconfig plip0 192.168.1.2 pointopoint 192.168.1.2
8). computer A-route 192.168.1.2 0.0.0.0 255.255.255 UH plip0
9). computer B-route 192.168.1.1 0.0.0.0 255.255.255 UH plip0
10). there are no plip timeout errors
11). ping never responds on either machine
12). tcpdump -i plip0 shows that the packets are getting
through, with an ``icmp: echo request'' but no reply. This is
the case on both machines.
13). netstat -i also shows the expected count on RX-OK for both
boxes, no errors or overruns.

So...there's no problem with the packets getting to each box...
it's as if the packets aren't dispatched thereafter.