[address-policy-wg] 2023-01 - New Version Policy Proposal (Reducing IXP IPv4 assignment default size to a /26)

On Thu, 2023-05-04 at 06:21 +0000, Matthias Wichtlhuber via address-
policy-wg wrote:
> > The problems in section 5 can be fixed easily, but it depends on
> > how the authors want to handle assignment upgrades / renumberings.
> > I'd suggest either dropping the 1Y utilisation requirement to e.g.
> > 40%, or else that if you reach e.g. 80% current usage, you qualify
> > to receive an assignment of 2x the current, up to /22.  Those
> > figures are plucked out of the air btw. The point with them is that
> > they are not 50%, which is obviously a magic number when the
> > natural increase of assignment size would be to double the size of
> > the block.
> 
> The goal of this part is to minimize renumberings while avoiding
> greedy requests. Dropping the one year requirement to 40% is
> reasonable if you think 50% is too harsh ("magic numbers"). We can
> incorporate this change.

I believe that what Nick was getting at was that 50% is "magic" in the
sense that it creates a problem:

 * a /24 has 254 usable addresses.
 * a /23 has 510 usable addresses -> half of that is 255.

So, suppose you have used 230 addresses out of your /24. You apply for
and get a /23 and happily renumber.

Then, after one year, you have used 254 addresses. This is less than
half of the /23 (510/2 = 255), so according to the rules you'd have to
downgrade back to a /24 again. You can now no longer grow, unless you
immediately apply for a /23 again.

So we either live with this "bug" and trust that whoever has to perform
evaluation is "reasonable", or we find a numbers that don't cause these
kind of edge cases.

Cheers,
Steven
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