Globally Unique Identifier - Part III

Bob Morris ram at CS.UMB.EDU
Fri Sep 24 08:37:57 CEST 2004

Richard Pyle wrote:

> ...
> Agreed!  And that might be the better approach (for a lot of reasons).  My
> only concern would be to what extent desktop database applications can uses
> MAC values as primary keys (compared to using something like long integers)
> efficiently and effectively, when manipulating large datasets in real time.
> I guess this may be a trivial point in the grand scheme of things -- but
> ultimately taxonomists will want to be able to work with large datasets on
> their personal computers.

eh??? MAC addresses /are/ just long integers.

Once reduced to a digital representation, /everything/ is just a long
integer. Hence in the end, for machine use, the differences between
different ID schemes come down to a very few criteria, all having to do
with programming ease and the effective computability of each of the
assertions about the acquisition of IDS and manipulations of them that
are required.]. No two schemes are distinguishable solely on the basis
that one of them appears to have a representation as integers and one of
them appears not to. What's more interesting is: for a given scheme, to
what representation other than as a long integer can you reduce the ID
and how does that help with the programming about, and administration
of, the identifiers, what is the scope of "Global" in the acronym GUID,
and what needs to be specified to convert the ID to another ID of
importance to the enterprise (e.g. converting a specimen guid to a

For example, MAC addresses were designed to be globally unique only
among devices on the same wire. They were historically assigned in
blocks to manufacturers of network interface cards, and the only
motivation to have no repetition was to insure that the NICs of two
manufacturers could be connected to the same wire. In fact, MAC
addresses are now routinely programmable and rarely designate some
worldwide distinction between two specific physical objects. Indeed,
anybody who buys a consumer router for home use is often---and sometimes
unknown to them---exposing to their ISP a MAC address for the router
hardware that is actually the MAC address of one of the NICs on their
internal network. Subject to the very criticism David V. has leveled
against them---lack of context /offered in the spec/---MAC addresses as
used on networks require for resolution into physical objects an Address
Resolution Protocol (ARP) that depends on the wire protocol. For
example, is the ARP for ethernet,
whereas is the ARP for
fibre channels. (Actually, ARPs are meant to select a MAC given some
other kind of identifier, usually a routing identifier like an IP
address. It's the Reverse ARP protocol that maps a MAC address to a
routing id, and protocol is the one that---through a layered series of
protocol translations---can eventually yield communication
with---although not the MAC address of---a temporarily unique physical

    "The Problem: The world is a jungle in general, and the networking
game contributes many animals.  At nearly every layer of a network
architecture there are several potential protocols that could be
used. " David C. Plummer, rfc826, November 1982

"RFC 826: it sucks big time. it's a piece of crap!! ", ando, 3/24/2004

"Protocol analysis in C01-AIM. The process was manual and laborious" ,
The Pandemonium of protocols, poster on network security found on the

Bob Morris

Little Bit O'History: Dave Plummer's address on RFC826 was Symbolics
Inc., one of two companies making Lisp Machines in the early eighties.
For reasons /really/ irrelevant to this discussion, Symbolics sold the
first and only brand of laser printer commercially available, a wet
toner device briefly manufactured by Canon. It came with nothing but a
bit mapped raster image processer and could barely be lifted by two
people. Within a year it was replaced by dry toner technology whose
general architecture is what laser printers look like today. At
Interleaf, Inc., I wrote some driver software for it. On the wall we
displayed my first output, meant to be some line art, and which we
titled "Blizzard in Antarctica". The second was titled "Coal Mine at

> ...
> Cheers,
> Rich

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