Is it safe to use 240.0.0.0/4

Wed Jun 17 22:38:32 UTC 2015

On Wed, Jun 17, 2015 at 5:38 PM, Ricky Beam <jfbeam at gmail.com> wrote:
> I'll wait for Curran to pop up with various links to reasons why Class E was
> "abandoned" by ARIN. (short answer: too much broken crap thinks it's
> multicast!)

Hi Ricky,

You may be confused. ARIN never possessed class E; it's held in
reserve by IETF. As much as I enjoy a good ARIN bashing, they and John
Curran are quite faultless here.

IIRC, the short answer why it wasn't repurposed as additional unicast
addresses was that too much deployed gear has it hardcoded as
"reserved, future functionality unknown, do not use." Following an
instruction to repurpose 240/4 as unicast addresses, such gear would
not receive new firmware or obsolete out of use quickly enough to be
worth the effort.

Given how slowly IPv6 is deploying, this choice may prove to have been
shortsighted. Had IETF designated class-E as "reserved, future
unicast" in 2008 when the issue was debated and asked vendors to
update their software to expect 240/4 to be used as unicast addresses,
half the problem equipment would already have aged out and we could
all be debating whether to make them more RFC-1918 or hand them off to
the RIRs.

Regards,
Bill Herrin

-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>