Hello Dan,
Here is a note I wrote myself some years ago, when I last tried
it. I like slip because it's simple and does the job. I will try
to test it this evening.
/etc/ifconfig.sl0
! /sbin/slattach -h -s 115200 /dev/tty00
inet 192.168.3.129 192.168.3.128 up
(IP addresses reversed at one end of the cable).
-Andy Ball.