[dhcwg] Re: [v6ops] Re: [IPv6]Re: Android now su pports DHCPv6 PD

On Wed, 17 Sept 2025, 01:03 Gert Doering, <[email protected]> wrote:

> Hi,
>
> On Tue, Sep 16, 2025 at 06:04:33PM +0900, Lorenzo Colitti wrote:
> > Recommendations for network operators are written in RFC 9663. Some text
> > about expected prefix lengths is in section 8 of that RFC. RFC 9762 says
> > the prefix must be SLAAC-sized, which currently means it must be a /64
> per
> > device. A /48 is fine for a small or medium network, but a campus with
> tens
> > of thousands of devices on it probably needs more than that.
>
> If but anyone had warned of this outcome before.
>

If you're worried about IPv6 address space running out, you might want to
have a look at the original IPv6 proposal in RFC 8507, which proposed a 64
bit address space.

IPv6 moving to 128 bits was not because 64 bits wasn't considered big
enough. It was to originally to support the GSE proposal,

https://datatracker.ietf.org/doc/html/draft-ietf-ipngwg-gseaddr-00

While GSE didn't eventuate, what did eventuate was another 64 bits on the
end of addresses, which gave us a simple, one-size fits all default /64
subnet size, iinstead of the error prone, complex, variable and potential
need to renumber "right-sized" subnets inherited from IPv4's CIDR - for
those who have no choice to do it. Most people do /24s when they can - from
within Class A and Bs originally, and then RFC 1918 when that public IPv4
address space became tight - because people used /24s.

It has now given us the ability to give each host in networks where it
would be useful a /64 each.

A /64 per host in a /128 address space is the equivalent of assigning a
single address per host in a 64 bit address space. It's more efficient than
what would have happened with a 64 bit address space - there would have
still been unused IPv6 64 bit addresses in the likely common /56 subnets
(i.e. IPv4 /24 equivalents).

A 64 bit address space is 4 billion times larger than IPv4's 32 bit address
space. Has there been any other time in humanity where when something
wasn't big enough the next biggest designed size was 4 billion times larger
than the previous size?

IPv4 was an experiment and proof of concept that escaped into production.
IPv6 is really the first true Internet Protocol for the world wide Internet
we have today and in the future.

If you're interested in the evolution and history of IP addressing,
starting from 1974, I did a presentation on it at NZNOG earlier this year:

https://www.youtube.com/watch?v=Q-sPQ7p5n9c&t=11546s

Regards,
Mark.




> Gert Doering
>         -- NetMaster
> --
> have you enabled IPv6 on something today...?
>
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