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

William Herrin bill at herrin.us
Sun Jun 27 10:31:56 EDT 2010

On Sun, Jun 27, 2010 at 7:10 AM, Eliot Lear <lear at cisco.com> wrote:
> You've covered a lot of the ground of the discussion.  I presented this
> draft on behalf of our author group to the int-area, and got pushback from
> the room in the following forms:

Hi Eliot,

Thanks for the report. Some comments...

> It would take forever to fix printers, fridges, and other appliances, along
> with routers, firewalls, and other middle boxes.

Part of my reason for preferring 240/4's use as private addresses is
that you can reasonably hope to control what goes on inside your own
network. Even with customers you can make a globally routable address
available for an extra fee so that folks with non-supporting equipment
don't have to ever see the private IP addresses.

On the public Internet 240/4 is dead weight. No one is going back to
fix Windows 98 and all the other legacy equipment that *will* be
present in enough quantity to cause a problem.

> /4 is a honking lot of private address space that would benefit few.

We'll see. This depends on the degree to which ISPs implement IPv4
carrier NATs which, at this point, is on everyone's long-range radar.

I also note ULA sets aside a larger percentage of IPv6's total address
space (a /7) for private addressing than is set aside out of IPv4's.
Perhaps it would be wise to carve out a /6 from 240/4 as "ISP-local"
private addresses and then see what happens before determining the
fate of the rest of the /4. No point making the same mistake as with

What isn't debatable is that we're approaching a dire shortage and
right now 240/4 is a honking lot of address space that benefits
exactly _nobody_.

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

Would you clarify this? You've emphasized it but I don't follow how
the use of 240/4 as unicast addresses (especially private unicast
addresses) disrupts any v6 protocols on the books.

> Better to focus on v6 transition.

Myopic. Unless another credible solution presents, IPv4 carrier NATs
-ARE- the v6 transition.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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