Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!NSIPO.ARC.NASA.GOV!medin
From: medin@NSIPO.ARC.NASA.GOV ("Milo S. Medin", NASA ARC NSI Project Office)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Using the 4.2 broadcast addr with 4.3 systems
Message-ID: <8909040520.AA21687@nsipo.arc.nasa.gov>
Date: 4 Sep 89 05:20:42 GMT
References: <NELSON.89Sep3103326@sun.clarkson.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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Well, I think you can legitimately say that link level tagging as
we are discussing does violate layering in that it is passing info
about link level info to the network layer.  As I understand it, you can
pass all the info you want to an upper layer, as long as you
don't pass info that is only known at your layer.  Consider passing
link level MAC addresses to IP, or passing IP checksum info to the
application.  Granted, these are extreme examples, but it does make the
point.  

This is why the ISO model is a model, and should not be construed as
an implementation guide :-)...  In general, all the layers in the world
won't help you unless you use common sense.

						Thanks,
						   Milo