[arin-ppml] Use of "reserved" address space.

James Hess mysidia at gmail.com
Sun Jun 27 14:58:16 EDT 2010

On Sun, Jun 27, 2010 at 6:10 AM, Eliot Lear <lear at cisco.com> wrote:
> It would take forever to fix printers, fridges, and other appliances, along
> with routers, firewalls, and other middle boxes.
If IP enabled fridges can no longer use the LAN, then so be it..

It may be hard to convince manufacturers of even new devices to  'fix'
 it, yes, but
forever is a long time.   And the time it takes is measured  starting
_from the time the block is no longer marked as special_.   Currently
deployed printers, fridges, and other appliances have not even been in
service using IPv4  forever.

Of course if  240/4's  special future-use status is retained, this
becomes a self-fulfilling prophesy. If it stays 'special', yes, many
existing and future appliances  will not become capable of using 240/4
IPs, ever.  If the block were unreserved, it could take 20 years from
now before 240/4  could become usable in practice for public
addressing, and it would still be worth it, to withdraw 240/4's
special status today, on that basis alone.

240/4 could still be extremely valuable, even if most of it were only
available for private addressing.
Regardless of any IPv6 transition attempts,  IPv4  will still be in
use 20 years from now,  and address space  is likely to still be

> /4 is a honking lot of private address space that would benefit few.
> /4 really doesn't buy us much time in terms of staving off or easing a  transition
It buys you something.     And any reduction in V4 space utilization
benefits all.
"What it buys"  us  are speculations about the future,  which are not
agreed upon.

It only makes sense to say that if you assume there will be a
transition off V4, which is definitely not guaranteed.

Because of the limitations of 240/4 space,  240/4  addresses would not
likely to be used in the same way as the rest of the IPv4 space.

For example,  they might be useful for routers that only communicate
directly with devices that support 240/4  address space,  such as
Point to Point links,   where the addressing  used at each end  is not

In that case, the  240/4  space is beneficial,  because it  displaces
some other use of V4 space, allowing (non-240/4) public address space
to be freed up  for  end hosts.

Large NAT deployments run into addressing difficulties, requiring
complex configurations and multiple NATs.
Availability of some 240/4  space for private use   can  reduce the
complexity and increase the scalability of large NAT deployments.

It's  not necessary to immediately make a decision on whether 240/4's
future use should be private IPs or public IPs.   The  exact usages
could be determined at a later date,  with  testing and careful
consideration,   vendors  of routers would no doubt need time to
repair their IP4 implementations.

I would suggest at least some small portions of  240/4  be allocated
to an IP registry  and get announced, for testing purposes.

> There are several v4/v6 transition protocols that base assumptions about
> private address space.

> Better to focus on v6 transition.

This is also not a technically sound justification  for keeping 240/4
marked as non-unicast reserved special.

None of the justifications provided   show possible harm  or reason
to  NOT allow  removal of the future use designation of 240/4.

All they seem to show is  doubts  regarding  the  eventual usefulness
of doing so.
Which are true --   we cannot be certain of the usefulness of
removing the future use  non-unicast designation of 240/4.

However   "we shouldn't even really try"   is not a good answer.
Especially when the doubts are just speculation.


More information about the ARIN-PPML mailing list