IPv4 Reclamation Algorithm==========================OVERVIEWIn May 2012, the ICANN Board ratified the Global Policy for Post ExhaustionIPv4 Allocation by IANA.  This policy called for the establishment of aRecovered IPv4 Pool, which contains fragments leftover in the IANA andspace that has been returned to the IANA by other means. The policy alsocalled for IANA to make allocations from the Recovered IPv4 Pool once thepool is declared active.The pool was declared active on 20 May 2014 when the first RIR had less than a /9 of IPv4 space in its inventory. The pool will also be declared active during “IPv4 allocation periods”, 6-month periods following 1 Marchor 1 September in each year.ICANN reported that we will use an open-source software program to perform the address selection process. This code implements the IPv4 reclamation policy.REQUIREMENTSThe Global Policy calls for the following:    When the Recovered IPv4 Pool is first activated and at the beginning    of each subsequent IPv4 allocation period, we will use software to    select 5 IPv4 allocation units (one for each RIR) from the current    IPv4 Recovered pool.    An IPv4 allocation unit is 1/5 of Recovered IPv4 pool, rounded down    to the next CIDR (power-of-2) boundary.    The minimum "IPv4 allocation unit" size will be a /24. If the    calculation used to determine the IPv4 allocation unit results in a    block smaller than a /24, the IANA will not distribute any addresses    in that IPv4 allocation period.The software should use the published ipv4-recovered-address-spaceregistry XML file as input and output an updated XML file for check-in tothe repository. Ideally, the software should try to allocate RIRs addressspace within /8s they already manage, based on the distribution in theipv4-address-space registry.METHODOLOGYThe algorithm determines the number of addresses that must be assignedto each RIR using the Global Policy. It determines the available rangesthat can be re-allocated using the IANA recovered IPv4 address registry.It also determines a preference for each range using the current "WHOIS"records in the IPv4 address registry. The WHOIS record is a good indicatorof which RIR is responsible for the covering /8 for a particular IPaddress.Based on these inputs, the algorithm iterates through each RIR and findsthe best record to satisfy their need. Allocations are weighted toward(a) allocations that would be drawn from a range for which theRIR is responsible for the covering /8; (b) allocations that are larger;and (c) allocations that are the exact size of the needed space.HOW TO USEThe algorithm is implemented as a command-line tool. Invoking the toolwithout arguments will fetch the most recent version of the two inputregistries from the IANA website. You can alternatively specify either afile-path or a URL as command line arguments to nominate alternate inputs.Using the "-o" or "--output" flags will save a revised version of therecovered IPv4 registry updated to reflect the new allocations. Note thatallocations generated by this software will only take effect once therevised registries are published officially by ICANN.LICENSECopyright (c) 2014, Internet Corporation for Assigned Names andNumbers. All rights reserved.Redistribution and use in source and binary forms, with or withoutmodification, are permitted provided that the following conditions are met:    * Redistributions of source code must retain the above copyright      notice, this list of conditions and the following disclaimer.    * Redistributions in binary form must reproduce the above copyright      notice, this list of conditions and the following disclaimer in the      documentation and/or other materials provided with the distribution.    * Neither the name of the ICANN nor the names of its contributors      may be used to endorse or promote products derived from this      software without specific prior written permission.THIS SOFTWARE IS PROVIDED BY ICANN AND CONTRIBUTORS ``AS IS'' AND ANYEXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THEIMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ICANN OR CONTRIBUTORS BELIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, ORCONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OFSUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESSINTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER INCONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OFTHE POSSIBILITY OF SUCH DAMAGE.