[RRG] Terminology redux

[RJ Atkinson <rja@extremenetworks.com>]

Earlier, Tony Li wrote:
% In any switched network, the MAC address is used
% for a lookup in the bridge table to determine
% destination location. Thus, it clearly also
% has some locator functionality.

Some general observations:
- Many modern edge links (e.g. IEEE 802.11*, pre-JTRS,
  IEEE 802.16*, EVDO/EDGE) are neither switched nor bridged.

- Also, some Ethernet cable (e.g. coax) deployments
  still exist, though I don't see them often any more.

- Integrated Ethernet switch+router boxes are common; it is
  most of what we sell these days in the purple universe.

- In turn, many deployments (govt, enterprise, service provider,
  & other) run with L3 routing all the way to the edge box,
  with each end node being directly connected to that edge box
  (i.e. there is no bridging on the edge sub-network, just
  really simple output interface selection).

% Indeed. It's pretty clear that we can still have semantic
% cleanliness tho, as we can isolate a particular bit string
% as having L3 identifier semantics (coupled with L2 locator
% and L2 identifier semantics) and distinct from L3 locator
% semantics.

In at least some technologies that are being discussed on
this list, the "Network-layer" Identifier does not have
L2 Locator semantics.

Whether one considers such an Identifier to have L2
Identifier semantics depends mostly on how one defines
the layers; just as it can be hard to distinguish
between the "top of the network layer" and the "bottom
of the transport layer".  Is ARP at the top of layer
2 or the bottom of layer 3 ?  What layer is MPLS in ?

Quite separately from the above, I'm inclined to agree
with Brian C that an IEEE MAC address is an identifier,
not a locator.  Unlike an IP address (either version)
or a CLNP address (any address format), there simply
is no topology (e.g. routing prefix) encoded into an
IEEE MAC.  It is just an opaque ID.  The MAC can be
used as an index into a flat database, but using it
as a flat-database index doesn't magically transform the
MAC into a Locator.  If there were topology embedded
inside the bits of the MAC, I'd likely take the opposite
view.

That noted, the "EID" (sic) in LISP is simultaneously used
both for identity and for location (e.g. inside the end
sites).  This community has a word for objects with mixed
semantics of both location and identity -- we've called it
an "address" for several decades.  (just to be very clear:
This is a comment about the confusing terminology used by
LISP documents and advocates, not a criticism of the LISP
technology itself. :-)

While I think that an Identity/Location split is one path
forward, I don't think it is the only possible path forward.

I do think that this group would serve itself well to
define -- and actually use here -- more crisp terminology.
A number of the threads here seem to derive from differences
in the definitions of words, rather than material technical
differences.

Cheers,

Ran

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