[dhcwg] Re: [IPv6]Re: [v6ops] Re: Re: Android now supports DHCPv6 PD

On 17 Sep 2025, at 10:16 am, Mark Smith <[email protected]> wrote:



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

There are many interpretations as to what happened and why in the 1991 - 1994 period in the work on what became IPv6. Some of these are from folk who were personally involved in the effort in various ways, others from those who came later and tried to make some sense out of the somewhat chaotic trail of material that the effort left in its wake. Mark's view here is certainly one such interpretation of this material, but there are certainly different interpretations as to how and why we landed up where we are today.

There is the view that fixed boundaries in an address plan is never a good idea, and we should be able to allow network operators to define an effective address plan to suit their particular requirements. There is another view that iits possible to define an address plan such that "one size fits all" -  I've personally lost faith in that latter view!

"first true Internet Protocol" - really??

Geoff

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