minimum IPv6 announcement size

Ryan McIntosh rmcintosh at
Fri Sep 27 06:10:47 UTC 2013

I don't respond to many of these threads but I have to say I've
contested this one too only to have to beaten into my head that a /64
is "appropriate".. it still hasn't stuck, but unfortunately rfc's for
other protocols depend on the blocks to now be a /64..

It's a waste, even if we're "planning for the future", no one house
needs a /64 sitting on their lan.. or at least none I can sensibly
think of o_O.


On Fri, Sep 27, 2013 at 12:57 AM,  <bmanning at> wrote:
>  Yup.  Seen/Heard all that.  Even tooted that horn for a while.
>  /64 is an artifical boundary - many/most IANA/RIR delegations are in the top /32
>  which is functionally the same as handing out traditional /16s.  Some RIR client
>  are "bigger" and demand more, so they get the v6 equvalent of /14s or smaller.
>  Its the _exact_ same model as v4 in the previous decade.  With the entire waste
>  in the bottom /64.
>  Its tilting at windmills, but most of the community has "drunk the koolaide"
>  on wasteful /v6 assignment.   What a horrific legacy to hand to our children
>  (and yes, it will hit that soon)
> /bill
> On Thu, Sep 26, 2013 at 01:18:50PM -0700, Darren Pilgrim 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.
>> 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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