minimum IPv6 announcement size

joel jaeggli joelja at
Thu Sep 26 20:36:07 UTC 2013

On Sep 26, 2013, at 1:18 PM, Darren Pilgrim <nanog at> wrote:

> On 9/26/2013 1:07 PM, joel jaeggli wrote:
>> On Sep 26, 2013, at 12:29 PM, Darren Pilgrim <nanog at>
>> wrote:
>>> On 9/26/2013 1:52 AM, bmanning at wrote:
>>>> sounds just like folks in 1985, talking about IPv4...
>>> The foundation of that, though, was ignorance of address space
>>> exhaustion.  IPv4's address space was too small for such large
>>> thinking.
>> The first dicussion I could find about ipv4 runnout  in email
>> archives is circa 1983
>>> IPv6 is far beyond enough to use such allocation policies.
>> There are certain tendencies towards profligacy that might
>> prematurely influence the question of ipv6 exhaustion and we should
>> be on guard against them… allocating enough /48s as part of direct
>> assignments  is probably not one of them.
> That's just it, I really don't think we actually have an exhaustion risk with IPv6.  IPv6 is massive beyond massive.  Let me explain.

Instead of explaining to me how awesomely big ipv6 is you might figure out who you're talking to, or maybe consider the problem a bit more.

Semantic addressing schemes can soak up as many bits as you're willing to give them.

ISP(s) using (for example) 6rd or other automatic prefix mapping mechanisms can potentially use rather large prefixes.

128 bits is not so many that we can't trivially soak them all up and we should not pretend otherwise. We are stewards of the resource and we should manage it with care that reflect's long term thinking, both so that allocations we make now are not inappropriately small in the future and such that we are not again confronting the shortcomings of our decision-making again in 20 years.

> We have this idea of the "/64 boundary".  All those nifty automatic addressing things rely on it.  We now have two generations of hardware and software that would more or less break if we did away with it.  In essence, we've translated an IPv4 /32 into an IPv6 /64.  Not great, but still quite large.
> Current science says Earth can support ten billion humans.  If we let the humans proliferate to three times the theoretical upper limit for Earth's population, a /64 for each human would be at about a /35's worth of /64's.  If we're generous with Earth's carrying capacity, a /36.
> If we handed out /48's instead so each human could give a /64 to each of their devices, it would all fit in a single /52.  Those /48's would number existance at a rate of one /64 per human, one /64 per device, and a 65535:1 device:human ratio.  That means we could allocate 4000::/3 just for Earth humans and devices and never need another block for that purpose.
> That's assuming a very high utilisation ratio, of course, but really no worse than IPv4 is currently.  The problem isn't allocation density, but router hardware.  We need room for route aggregation and other means of compartmentalisation.  Is a 10% utilisation rate sparse enough?  At 10% utilisation, keeping the allocations to just 4000::/3, we'd need less than a single /60 for all those /48's.  If 10% isn't enough, we can go quite a bit farther:
> - 1% utilisation would fit all those /48's into a /62.
> - A full /64 of those /48's would be 0.2% utilisation.
> - 0.1%? We'd have to steal a bit and hand out /47's instead.
> - /47 is ugly.  At /52, we'd get .024% (one per 4096).
> That's while maintaining a practice of one /64 per human or device with 65535 devices per human.  Introduce one /64 per subnet and sub-ppm utilisation is possible.  That would be giving a site a /44 and them only ever using the ::/64 of it.
> Even with sloppy, sparse allocation policies and allowing limitless human and device population growth, we very likely can not exhaust IPv6.

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