Re: 240/4 unreservation (was RE: Last Call: <draft-weil-shared-transition-space-request-03.txt> (IANA Reserved IPv4 Prefix for Shared Transition Space) to Informational RFC)

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Frank Ellermann wrote:

Oops, I failed to send the following to the list.

> Updating RFC 1112 (STD 5)
> or maybe RFC 1166, and then RFC 5735 for 6.25% of all windmills minus
> one.

Updating RFC1112 is not necessary because, even though it says:

   *    a datagram whose source address does not define a single
        host -- e.g., a zero address, a loopback address, a
        broadcast address, a multicast address, or a Class E
        address.

Class E is an example and, more interestingly, the rule is silently
ignored by ICMPs generated against private use addresses, which
do not define single hosts.

Updating RFC can be as simple as follows:

   240.0.0.0/4 - This block, formerly known as the Class E address
   space [RFC1112], and was reserved for future use [RFC5735] is
   now allocated for use in IPv4 unicast address assignments with
   default netmask of 0xffffffff.

   The addresses in the block is not special use IPv4 addresses
   anymore.

   There are two exceptions to this.

   One exception is the "limited broadcast"
   destination address 255.255.255.255.  As described in [RFC0919]
   and [RFC0922], packets with this destination address are not
   forwarded at the IP layer.

   Another exception is the "shared transition" block
   of 240.0.0.0/12, which is set aside for use in private ISP
   (not end user) networks. Its intended use is to be documented
   in a future RFC, As will be described in that RFC, addresses
   within this block do not legitimately appear on the public
   Internet. These addresses can be used without any coordination
   with IANA or an Internet registry.

                        Masataka Ohta
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