The Reg does 240/4

Tue Feb 13 23:06:51 UTC 2024

On Tue, Feb 13, 2024 at 2:34 PM Christopher Hawker <chris at thesysadmin.au> wrote:
> Having [240/4] reclassified as unicast space is indeed much easier.

Hi Chris,

If I were spending my time on the effort, that's what I'd pursue. It's
a low-impact change with no reasonable counter-argument I've seen. As
you noted, half the vendors already treat it as unicast space anyway.

> With that, comes the argument - what about legacy hardware
> that vendors no longer support, or are out of warranty and no
> longer receive software updates?

What about legacy hardware that doesn't support CIDR? What about the
1990s Sparc Stations that don't have enough ram to run anything
vaguely like a modern web browser? You make the key standards change
(from reserved undefined use to reserved unicast use) and over time
varying potential uses for those unicast addresses become practical
despite the receding legacy equipment.

None of us has a crystal ball saying when IPv4 use will start to fall
off. It's entirely possible It'll still be going strong in 20 more
years. If so, and if 240/4 was defined as unicast now, it'll surely be
practical to use it by then.

Making the simple standards change also lets us debate the "best" use
of the addresses while the needed software change happens in parallel,
instead of holding up the software changes while we debate. Allocating
them to the RIRs isn't the only practical use of a new set of unicast
IP addresses. Other plausible uses include:

* More RFC1918 for large organizations.

* IXP addresses which only host routers, not the myriad servers and
end-user client software.

* ICMP unreachable source address block, for use by routers which need
to emit a destination unreachable message but do not have a global IP
address with which to do so.

* A block of designated private-interconnect addresses intended to be
used by off-internet networks using overlapping RFC1918 which
nevertheless need to interconnect.

Indeed, the only use for which we definitely -don't- need more IPv4
addresses is Multicast.

So, a rush to deploy 240/4 to RIRs is not really warranted.

Regards,
Bill Herrin

-- 
William Herrin
bill at herrin.us
https://bill.herrin.us/