Making Use of 240/4 NetBlock

Masataka Ohta mohta at
Fri Mar 11 04:44:21 UTC 2022

William Herrin wrote:

>> Ever since we started our study, we were quite puzzled by why the 240/4
>> netblock was regarded so special? Why no one could tell us what led to
>> its current status, and even after IPv4 was set to transition to IPv6?

> Which leads to RFC 1112 section 4, the disposition of which last
> changed in 1989.

IIRC, at some time, perhaps when CIDR was deployed widely and
having something other than IPv4 was a hot topic, there was a
discussion on releasing 240/4 in IETF. Reasonings against it were
that the released space will be consumed quickly (at that time,
NAT already existed but was uncommon) and that new IP will be
designed and deployed quickly (we were optimistic).

						Masataka Ohta

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