Making Use of 240/4 NetBlock

William Herrin bill at
Sun Mar 13 23:55:20 UTC 2022

On Sun, Mar 13, 2022 at 12:29 PM Christopher Morrow
<morrowc.lists at> wrote:
> What's the actual proposal for 240/4?
> Is it: "Make this usable by me on my /intranet/?"
> Is it: "Make this usable across the internet between bespoke endpoints?"
> Is it: "Make this usable for any services/users on the wider internet, treat it like any other unicast ipv4 address?"

Hi Chris,

I can't speak for anyone else but my proposal is: (A) do the
standards-level activity which is common to all three proposals, (B)
give the vendors a couple years to catch up to the new standard, and
then (C) pick a next step based on what's then the operational

The standards-level activity common to all three proposals is:

1. Define 240/4 excluding as unicast addresses (no
longer "undefined" future use) but continue holding them in reserve.
2. Advise hardware and software vendors to treat 240/4 as unicast when
configured by the user or received by protocol.
3. Stop.

Bill Herrin

William Herrin
bill at

More information about the NANOG mailing list