[RRG] Re: Should the identifier be used as local locator

[Christian Vogt <christian.vogt@nomadiclab.com>]

Brian and Tony -


> > Brian wrote:
> >
> > But you're correct too. Whether a bit string is a locator or an
> > identifier depends entirely on context. (That's why I've objected to
> > EIDs in LISP being called EIDs from the start - once they hit the  
> > site
> > network, they become locators instantaneously; they are only
> > identifiers in the global context.)
>
> Tony wrote:
>
> 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.


You define the terms "identifier" and "locator" based on whether you
can route on them.  This is why an identifier can become a locator, or
vice versa, if you look at it in a different context.

Hitherto, my definition of the terms was independent of whether you
route on them or not:  I thought of a "locator" as a place in network
topology, and of an "identifier" as a name for a host (or for some
entity on the host such as an interface card or an application
session).  In other words, given an attachment point to the network, a
the locator described something on the network side of it, and the
identifier described something on the host side of it.  With this
definition, whether a name is an identifier or a locator does not
change with the context.

Decoupling what a name describes from what you can do with the name is
sensible IMHO because only the latter depends on the context:  Within
small scope, routing based on identifiers may certainly be feasible. A
good example is the bridge you mentioned, which maps MAC addresses
(which are identifiers according to my definition) onto "next-hops".
For global scope, routing based on identifiers fails due to
scalability issues because identifiers cannot facilitate aggregation
of next-hop information in routers or switches due to host mobility
and multi-homing.  Locators do facilitate such aggregation, provided
they have a suitable structure, which is why they are more appropriate
for global-scope routing.

Anyway, I have no problems changing my definition if the research
group wants to use a different one.  Let's just agree on one of them.

- Christian



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