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Re: [RRG] Terminology redux



On 7/8/08 10:15 AM, RJ Atkinson allegedly wrote:
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 ?

ARP is an "adaptation function", to facilitate one layer network running over another.

What layer is MPLS in ?

Intra-domain MPLS is just an encapsulation for specialized carriage of packets over an IP network. Inter-domain MPLS is a layer network (see previous ITU reference).

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.

This depends on how it's used. An IP address does not have any topology encoded into it either. Rather, we assign IP addresses in line with the topological hierarchy, and interpret addresses accordingly in routing. That is not an intrinsic property of the address.

But the main point is that you can use anything as input to your location function or your identification function. That's not a good criterion. What you need is not identifiers that are not used for location purposes (that gets us into these terminology cycles), but rather: names that are location-independent in the context of the routing and addressing architecture under consideration, and thus can be used as identifiers. An architecture that makes having those easier is a good thing.

Scott

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