Subject: RE: Globally Unique Private Addresses and Scoped Architecture

From: "Michel Py" <[email-masked]>
Date: Thu, 10 Apr 2003 10:01:40 -0700

Charlie,

> Charlie Perkins wrote:
> But global uniqueness means we don't need scoping in the
> (unicast) address architecture. It means that scoping can
> be done as part of route table management instead.

Can you give some precisions about this?

> I think we need addresses that are not allowed to be
> "globally routable", but are still unique. I certainly
> agree that these addresses should still be routable
> according to the needs of the local administration.

Yes.

> To be precise, though, we do want non-routable addresses
> too; they're the link-local addresses.

Yes.

Michel.

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From: "Charles E. Perkins" <[email-masked]>
Date: Thu, 10 Apr 2003 10:13:38 -0700

Hello Michel,

> Can you give some precisions about this?

To be precise, needs precise definitions.  Shall I be so bold?

Let's say that a "scope" corresponds to a "domain of effectiveness".
Now we have two undefined terms instead of just one.  Ignoring
that for the moment...  (and, so much for precise definitions!)

Applied to a globally unique address (note: not necessarily
globally routable) it means the networks where the address
may be used to support communications.  For addresses that
aren't globally routable, I reckon this would mean those
networks where non-global arrangements have been made for
routability.

That means that the "scope" of the address is defined by the
(non-global) routing arrangements that have been made for
that address.

I hope this is helpful.  It's probably crucial to get some
definitions that are agreeable, and that help to decompose
what could currently be viewed as a mass of related but
separable wishlist items.

Regards,
Charlie P.

---

From: Tim Chown <[email-masked]>
Date: Thu, 10 Apr 2003 20:21:29 +0100

OK, so Steve isn't with us to give his comment.  But I was curious to see
what he might have said in the past.  The Google is Your Friend.

First, it is interesting that in 2003 people think that deleting site-locals 
will send the wrong message about IPv6 readiness.   Just look what Steve 
himself said in March 1998... 

"Well, it does appear that we do not have consensus on deleting site-local
 addresses from IPv6.  Also, someone mentioned to me another reason for
 retaining site-locals: deleting them at this point would just strengthen
 a preception in some quarters that IPv6 is still undergoing significant
 changes, and therefore is not ready to be taken seriously.  While I
 personally think that deletion of inessential features is a much more
 benign type of change than addition of new features, and that as a living,
 evolving technology, it is wrong to expect IP ever to be "done", it
 is nonetheless important for us to be sensitive to the concerns people have
 about its stability.  So for that reason and the other reasons people have
 identified, I propose that we keep site-local addresses for now, and
 continue to work on ironing out the details of their use."
(http://www.cs-ipv6.lancs.ac.uk/ipv6/mail-archive/IPng/1998-04/0085.html)

That was 1998.  We've since had 5 years to "iron out details of their use" 
but haven't done so yet, although Brian and some others have some scoped
implementations.

Also in March 1998, in response to Christian's suggestion of the evilness
of scoped addresses, Steve wrote:
 
"Site-local addresses made more sense in some of the earlier stages of
 SIP and SIPP development, based on ideas that no longer apply in IPv6.  I
 would be quite happy to delete site-local unicast addresses entirely from
 IPv6 if we had consensus on that (though the notion of site boundaries would
 still appear in the scope field of multicast address) -- it would simplify
 the implementations and the specs, and eliminate much of the confusion and
 design choices of the sort we have been discussing.  However, I don't recall
 consensus ever being reached about net 10 in the IPv4 world.  Does anyone in
 the IPv6 community want to speak up in favor of site-local addesses?

 (Note: if we eliminated site-local addresses, we could always add them back
 in in the future if absolutely necessary, using the net 10 approach, i.e.,
 simply designating one global prefix for private use.)

 (I realize that I probably sound rather inconsistent here, on the one hand
 arguing for flexibility in how site-local address may be used, and on the
 other hand being content to see them eliminated altogether.  But I don't think
 I am contradicting myself: I prefer the minimum number of mechanisms that
 achieve the maximum "power"/capability/generality.  *If* we are going to
 keep site-local addresses, I think we should not unnecessarily constrain
 their possible use.)"
(http://www.cs-ipv6.lancs.ac.uk/ipv6/mail-archive/IPng/1998-04/0033.html)

So (again five years ago) Steve was happy to write out site-locals if we
have consensus to do so, on the basis that we can always add them back
later if the alternatives don't work out.

Also note we would keep site local multicast scope - something which itself
could be used for some service discovery mechanisms.

Of course I wouldn't presume that Steve's views would be the same now, but
I found it interesting to read what he write, even five years ago,
particularly the second quote.

Tim