Subject: Re: [RAM] Re: Ramblings about "locator"

From: [email-masked] (Noel Chiappa)
Date: Thu, 14 Jun 2007 15:30:23 -0400 (EDT)

> From: Dino Farinacci <[email-masked]>

    > a MAC address is certainly used to find (that means "where", and
    > "where" means location) an ethernet attached station in a L2 switched
    > network.
    > ...
    > remember OSI and what an L1 area in IS-IS was used for? To route
    > system-ids which were based on MAC addresses. So in this case, the MAC
    > was a locator.

I have a hard time figuring out what "locator" means to you all if you think
a MAC address is a locator.

To me, a name cannot be a locator (or have 'location semantics') unless it
has the property that when the thing being named moves to a new location, it
needs a new locator (since the locator says 'where' it is). MAC addresses
explicitly do not have this property; they *always* stay they same *no matter
where* you plug them in and/or move them.

Ergo, they are not locators, and have no location semantics.

As I said in my previous message:

  .. just because a name identifies a thing which is at a particular location
  (e.g. an interface), that does not mean that the name has 'location
  semantics'. To me, there has to be *information* in the name (so that e.g.
  it can pass the 'are [the things named by] these two [names] close [to each
  other]' test).

To put it another way, *everything* has a location (or a set of them, e.g.
for replicated/distributed objects), and if "locator" simply means 'name of a
thing which has a location', that's a non-useful tautology, kind of like
saying 'name of a thing which has a name'.

	Noel

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From: RJ Atkinson <[email-masked]>
Date: Thu, 14 Jun 2007 16:30:35 -0400

On  14 Jun 2007, at 15:30, Noel Chiappa wrote:
> I have a hard time figuring out what "locator" means
> to you all if you think a MAC address is a locator.

Noel,

	You were the person who persuaded me, after some
resistance on my part, that since the IEEE MAC address
is used in a lookup table (either a bridge table or an
IPv6 ND table) to forward the frame/packet, therefore
the MAC address must have location semantics and so
could not be a pure Identifier.

	Now, you've changed horses and are riding away
in the opposite direction.

	I am pretty confused at this point about what your
perspective is.  I gather your thinking has evolved since
this precise question last came up.

Cheers,

Ran

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From: Tony Li <[email-masked]>
Date: Thu, 14 Jun 2007 13:47:11 -0700

> could not be a pure Identifier.

If we consider forwarding functionality to be the definition of a  
locator, then we are going to have a very serious issue.  Consider  
other forwarding mechanisms that let you take into account source  
address, port number, protocol number, DSCP, etc. as part of the  
forwarding decision.  If we follow that logic, the phase of the moon  
could also be a locator.  Is that what we want?

I prefer Joel's line of thinking.

Tony

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From: Peter Sherbin <[email-masked]>
Date: Fri, 15 Jun 2007 06:23:38 -0700 (PDT)

> locator, then we are going to have a very serious issue.

The above should not be a constrain or concern because in the new architecture under
discussion all current principles may not need to apply. E.g. current address vs.
future id / loc split.

Thanks,
Peter

> I prefer Joel's line of thinking.

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From: Mikko Särelä <[email-masked]>
Date: Mon, 18 Jun 2007 16:08:06 +0300

> could not be a pure Identifier.

Names such as MACs can be used to point to a location in the network
topology. However, the important question is not whether they can be
used, or even if they are used for such a thing. The important
distinction between two types of names is whether the names themselves
carry topological significance.

In the case of IP addresses, the name itself carries topological
meaning. In the case of MACs the names carry no topological meaning. The
network, however, uses those names to make a map of the network topology.

The difference between these two cases is that in the former, the name
itself carries part of the topological information, where as in the
latter all the information resides in the bridge.

-Mikko