Regarding MAC address as a machine key.
I suspect that you could take md5(MAC_Address || IPV4_Address) to create a
machine ID which you can reasonably expect to be unique (i.e. the chance of
having 2 identical MAC addresses on the same IPV4 address is small enough to
disregard). I only suggest using MD5 to hide the details of the MAC and
IPV4 address from the outside world, and it is not strictly necessary for
the purposes of this discussion.
Best Wishes,
Chris Travers
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