[arin-ppml] IPv6 policy: limitations on registrants?

[William Herrin]

On Sun, Jun 28, 2026 at 2:04 PM John Osmon <josmon at rigozsaurus.com> wrote:
> On Thu, Jun 25, 2026 at 03:29:15PM -0700, William Herrin wrote:
> > Should they have to be for use on the Internet with off-Internet uses
> > expected to use something like ULA? Or are off-Internet uses just as
> > qualified as Internet uses?
>
> I'm a proponent for unique address space at all times.  Even an
> "off-Internet" network might need to interconnect with a new network
> (or, even, the Internet).
>
> Allowing unique address assignment means that if (when) such
> interconnection occurs, the formerly private network can coexist.

Hi John,

I take your statement to mean you favor off-Internet use being a valid
justification for ARIN IPv6 address registrations. Is that correct?

Bear in mind that IPv6 Unique Local Addresses under RFC 4193 are not
the same as RFC 1918. Like the rest of IPv6, the address space is much
larger and as the name implies the intent is that few if any users
select the same addresses. A simplification of the ULA rules boils
down to: generate a random number between zero and a trillion and then
add "fd" at the front. That's your /48 within fd00::/8. The birthday
paradox means overlap is not as unlikely as it might seem, but overlap
is still pretty unlikely.

That said, having ARIN assign an address block guarantees that you
won't accidentally overlap without relying on any stochastic foibles.

With this additional information, what are your thoughts?

Regards,
Bill Herrin


-- 
For hire. https://bill.herrin.us/resume/