On Wed, 2003-03-26 at 16:38, Tony Hain wrote:
Ted Hardie wrote:
I think you may underestimate how much trouble this might cause in
applications.
As Dave Crocker noted in response to Margaret Wasserman's
presentation to the APPs Open Area meeting, applications have
been designed so that
they
do not know and don't need to know anything about network
topology.
If you
require applications to understand the consequences of different
unicast address
scopes, you are changing a pretty fundamental assumption.
While it is
theoretically
possible to change that assumption, it is a major piece of
work, and I
believe that
the "sense of the room" was that the advantages of Site Local
were not
worth that
amount of work.
I am not arguing that every app need to know about topology. If this is
such a big deal, we should simply fix the API so that by default it only
returns global scope addresses, then add a new function for those apps
that are interested in the limited scope. This doesn't sound like rocket
science, and the arguments against it are coming across like 'we don't
want to change because it is too much work'. Rather than argue that
nobody can ever use a new feature, the basic approach should be that you
don't have to unless you want to.
Its not that 'we don't want to change because its to much work'. Its
that the Internet architecture assured us that the hour glass model
applied, that the network topology would remain abstracted within what
to us is an opaque address space. One of the number one reasons its so
easy for new application layer technologies to be deployed is that a
developer doesn't need to know or care about any layer below TCP (or, in
rare cases, UDP). If the lower layers want to change that hour glass
model then we're talking about a serious breach of contract with the
layers above it and a dangerous blow to the hour glass model.
-MM