the plipbox source is heavily based on the magPLIP driver found on aminet.net:

http://aminet.net/package/comm/net/magPLIP38.1

magPLIP - SANA II compliant PLIP device driver for AmiTCP/IP, Envoy,
	    AS225 and other networking packages

  (C) Copyright 1993-1994 Oliver Wagner, Michael Balzer
  (C) Copyright 1995 Jan Kratochvil & Martin Mares
  (C) Copyright 1995-1996 Marius Groeger
      All Rights Reserved.

  Changes have been made by Stéphane Zermatten to the driver to connect
  a LinuxBox to an Amiga via a LapLing cable, based on the release 37.8.