CC: s to Non List Members (was Re: 202203080924.AYC Re: 202203071610.AYC Re: Making Use of 240/4 NetBlock)

William Herrin bill at
Tue Mar 8 21:11:58 UTC 2022

On Tue, Mar 8, 2022 at 12:34 PM John Levine <johnl at> wrote:
> FWIW, I also don't think that repurposing 240/4 is a good idea.  To be useful it would require
> that every host on the Internet update its network stack,

Hi John,

That's incorrect and obviously so. While repurposing 240/4 as general
purpose Internet addresses might require that level of effort, other
uses such as local LAN addressing would only require the equipment on
that one lan to be updated -- a much more attainable goal.

Reallocating 240/4 as unpurposed unicast address space would allow
some standards-compliant uses to become practical before others. A few
quite quickly.

> which would take on the order of
> a decade, to free up some space that would likely be depleted in a year or two.  It's basically
> the same amount of work as getting everything to work on IPv6.

Is it not past time we admit that we have no real idea what the
schedule or level of effort will be for making IPv6 ubiquitous? This
year it was more than last year and next year it'll probably be more
than this year. The more precise predictions all seem to have fallen

Bill Herrin

William Herrin
bill at

More information about the NANOG mailing list