[ppml] IPv6>>32

[Michael.Dillon at radianz.com]

> o Increasing the HD ratio, or a flat utilization threshold fixes
>    any possible shortage.  If that doesn't do it, /48 -> /56
>    would.  The more I look at the numbers, the more convinced I
>    am that /48 should be left alone and a flat threshold be used
>    (perhaps 60%).

I agree that the /48 --> /56 issue is definitely second priority.
If we can solve the immediate problem by adjusting the HD ratio
rules then we should limit current action to that area.

I also think that a flat threshold is useful, but not in place
of the HD ratio. My thinking is that whatever the HD ratio is,
we should have a cap on the number of IPv6 addresses that we
allocate all in one go. Here's the scenario I envisage:

1. Network Operator comes to ARIN and says, I want to start
   deploying IPv6. ARIN looks at plans, forecasts, diagrams,
   and comes up with /12 as the right size allocation. But the
   cap rule kicks in and they only allocate this organization
   a /28.

2. Network operator goes away and works on deployment. A few
   years later they come to ARIN and show that they deserve 
   more addresses. At this point the HD ratio shows whether
   or not their /28 is densely used. If we adjust the HD ratio
   to .94 then this /28 will be a lot more densely used that
   it would have to be at a .8 ratio. Chances are this .94
   ratio means that step number two happens later than it
   otherwise would have. But the cap makes step number two
   happen earlier than it would have. In any case, ARIN sees
   that a /12 is still justified and allocates an additional
   /28 because of the cap. Operator is given the choice of
   renumbering into a new /27 if they wish to.

3. Network Operator returns a second time, rinse and repeat.
   But eventually, confidence in v6 renumbering is high and
   the network operator renumbers one of its /28 blocks into
   a new /27.

4. Network Operator returns a third time and receives a /26
   block. They then renumber out of their last /27 and their
   remaining /28.

Of course, the choice of /28 was purely arbitrary on my 
part to use as an example.

--Michael Dillon