Re: Microsoft and MACs

[Dan Strychalski <dski@ms17.hinet.net>]

Eric Bennett <ericb@pobox.com> wrote --

> First generation PowerMacs, sold in 1994-95, were compatible with Apple LAN
> utility.  There are plenty of those machines out there.  Whether this fits
> your definition of modern or not I don't know, but I think there are enough
> of these machines out there that anybody who wants to impersonate your MAC
> address could get ahold of one very easily.

The media access control (MAC) address, on an Ethernet device at least,
consists of six bytes. A manufacturer of Ethernet devices registers with
the Institute of Electrical and Electronic Engineers (IEEE) and receives
a set of values to use in (I think) three of those bytes on all its
devices; it then assigns values to the remaining bytes on a per-device
basis.

Communication on a LAN is done via packets. A packet is a chunk of data
in a wrapper called a frame. The sender's MAC address is part of the
frame. If firmware residing on the network interface card (NIC)
constructs each frame, there might be no way to change the MAC address
that the NIC uses. If a RAM-resident driver constructs each frame --
first getting a MAC address from the NIC, under normal circumstances at
least -- it could be made to insert any MAC address desired.

If those PowerMacs take NICs that can also be used in other kinds of
machines, we can assume that the driver reads the MAC address from the
NIC and ordinarily inserts that MAC address in frames it constructs. It
follows that a driver conceivably can be made to insert any MAC address
at all, regardless of what kind of system it is written for.

If that is the case, we see once again: it's all in the software.

(I once asked a networking specialist if there are NIC makers using
non-IEEE-approved MAC addresses. He seemed surprised that I thought it
necessary to ask.)

Dan Strychalski