[arin-ppml] Controlling the IPv6 address consumption rate

William Herrin bill at herrin.us
Wed Oct 13 10:43:37 EDT 2010

On Sun, Oct 10, 2010 at 12:08 PM, Owen DeLong <owen at delong.com> wrote:
> On Oct 10, 2010, at 7:09 AM, William Herrin wrote:
>> 7 billion people in the world, each of which consumes Internet
>> service, so as a lower bound we'll need 9 bits worth of 20M-equivalent
>> ISPs to serve them.
> 4,200,000,000 / 20,000,000 = 210 = 8 bits worth of 20M-equivalent
> ISPs. However, it won't actually work out that way. The vast majority
> of ISPs will be much smaller and there will be many more of them.

Okay. 8 bits, 9 bits. The key result from all the math is this:

Between an austere deployment of IPv6 (/60 end users, cramped routing,
etc) and a deployment of IPv6 that will consume the entire address
space prior to the retirement of IPv4, we have roughly 22 bits, not
the 96 bits that one might naively expect with an expansion from 32 to
128 bits.

Responsible management demands that we treat some portion of that 22
bits as a consumption suppressor so that we don't quickly run out of
IPv6 addresses. Whatever is left over, be it 4 bits, 20, or anything
in between, that's the number of bits we can actually afford to use
for nice-to-haves, like a larger standard end-user assignment than /60
(/56 or /48), sparse assignment and so on.

>>: how should we divvy up the 22 bits
>> between IPv4's consumption rate and IPv6's minimum needful consumption
>> rate? How many bits of convenience and how many bits of responsibly
>> slow consumption?
> _IF_ I understand what you mean by these terms correctly, then, yes,
> I think an 8/14 ratio isn't such a bad ratio

It sounds to me like you do understand what I mean.

8 bits of conservation worries me. We badly underestimated at the
start of IPv4. I'd be more comfortable starting with a more
conservative number (like 12 or 16) and then working down to 8 bits of
conservation after we gain a decade or two of experience.

On the other hand, if the current address consumption rate holds at
what eyeballs to me vaguely like 0.6(n^2), 8 bits of conservation
should buy us around 115 years. If Geoff is lurking, I'm sure he can
provide better information assuming completion of the IPv6 transition
with IPv6 consumption at 1/256th of IPv4's current consumption and the
same consumption growth rate exhibited over the last 15 years in IPv4.

Anyway, let's run with 8 bits and see what it implies.

8 bits means that the maximum allocation we can allow a single
organization to seek both initially and due to prior consumption is
/20. The largest holding we can allow an affiliated set of
organizations (including merged and acquired ISPs) totals /16. The
4-bit difference comes from that hold-against-development set I talked
about. Larger allocations than this, regardless of cause, are likely
to see us deplete the IPv6 free pool faster than the 8-bits
conservation target we've set.

8 bits also means you have only 14 bits left for the nice-to-haves. If
you spend 12 of those bits bringing the downstream end-user assignment
from the austere /60 to your preferred /48, you'll have only 2 bits
left. That doesn't give you much flexibility with your routing. Are
you sure you wouldn't rather put 4 of your bits to bring the
assignment up to /56 and use the remaining 10 to do smarter things
with your routing hierarchies? 256 LANs is a lot of LANs for all but
the largest customers.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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