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

Mark Andrews marka at
Wed Mar 9 04:28:29 UTC 2022

Given the draft lies about the status of 127/8.  Words have meanings.

   When all of was reserved for loopback addressing, IPv4
   addresses were not yet recognized as scarce.  Today, there is no
   justification for allocating 1/256 of all IPv4 addresses for this
   purpose, when only one of these addresses is commonly used and only a
   handful are regularly used at all.  Unreserving the majority of these
   addresses provides a large number of additional IPv4 host addresses
   for possible use, alleviating some of the pressure of IPv4 address

It is not RESERVED, it is ASSIGNED.

	 The class A network number 127 is assigned the "loopback"
         function, that is, a datagram sent by a higher level protocol
         to a network 127 address should loop back inside the host.  No
         datagram "sent" to a network 127 address should ever appear on
         any network anywhere.

If it was actually reserved there would be much less complaint.  People
have made use of that space based on the fact that it was ASSIGNED a
purpose whether you like that or feel that it was a good use of resources.

Compulsory acquisition is something that should not be done lightly.  It
also requires fair compensation to be paid.

> On 9 Mar 2022, at 13:35, Seth David Schoen <schoen at> wrote:
> John R. Levine writes:
>> This still doesn't mean that screwing around with 240/4 or, an even worse
>> 127/8 minus 127/24, is a good idea.
> I hope you'll be slightly mollified to learn that it's actually 127/8
> minus 127/16.
> That's the most challenging one, but we've still seen something of a
> lack of people getting in touch to point out concrete problems.
> One person did get in touch to describe an unofficial use of, apparently,
> all of 127/8 as private address space in a VPN product.  If people let
> us know about more, we can investigate workarounds or possible changes
> to our proposals.

What’s “unofficial” about it?  The point of ASSIGNING 127/8 for loopback
meant the ANYONE could use that address space OFFICIALLY so long as packets
with those addresses didn’t leave the machine.

> We previously thought that the reference NTP implementation was using
> all of 127/8 to identify hardware clock drivers.  But it turns out it
> doesn't actually connect to these.
> If anyone reading this knows of something that uses a loopback address
> outside of 127/16 for an application, or something that can't be updated
> and would be harmed if the rest of the network stopped treating this as
> loopback, we'd be glad to hear about it.

What does it matter what people are using those addresses for.  They are
using them in good faith and are under no obligation to report how they
are using them.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at

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