[e2e] use of MAC addresses

[Bob Braden]

John,

That line of reasoning (Saltzer plus) does not seem to clarify
a central distinction: media-dependent addressing vs.
media dependent addressing.  No one thought about building one
universal address space for media addresses, because we assumed
that each distinct medium would naturally have its own form
of addressing.  (Today, there is a tendency for (almost) all
media to look like Ethernets, so perhaps one exploit that
fact).  IP addresses were built to provide a universal
address space, with essentially an indirection linking to the
corresponding media-dependent addresses of connection points.

Bob Braden