IPv6 Address Allocation and Assignment Policy

-------------------------------------------------------------------- APNIC Document identity Title: IPv6 address allocation and assignment policy Short title: ipv6-address-policy Document ref: APNIC-089 Version: 010 Date of original publication: 1 July 2002 Date of this version: 9 August 2011 Review scheduled: n/a Obsoletes: Previous versions Status: Active Comments: n/a -------------------------------------------------------------------- IPv6 Address Allocation and Assignment Policy Status of this Memo This document was initially developed through joint discussions among the APNIC, ARIN and RIPE communities. The document also incorporates APNIC-specific policies developed since that time. Abstract This document defines registry policies for the assignment and allocation of globally-unique IPv6 addresses to ISPs and other organizations. This document obsoletes the "Provisional IPv6 assignment and allocation policy document". This document was developed jointly by the communities of APNIC, ARIN, and RIPE. Contents 1. Introduction 1.1 Overview 2. Definitions 2.1 Internet Registry (IR) 2.2 Regional Internet Registry (RIR) 2.3 National Internet Registry (NIR) 2.4 Local Internet Registry (LIR) 2.5 Allocate 2.6 Assign 2.7 Utilization 2.8 HD-Ratio 2.9 End site 2.10 Internet Exchange Point (IXP) 3. Goals of IPv6 address space management 3.1 Goals 3.2 Uniqueness 3.3 Registration 3.4 Aggregation 3.5 Conservation 3.6 Fairness 3.7 Minimized Overhead 3.8 Conflict of goals 4. IPv6 Policy Principles 4.1 Address space not to be considered property 4.2 Routability not guaranteed 4.3 Minimum Allocation 4.4 Consideration of IPv4 infrastructure 5. Policies for allocations and assignments 5.1 Initial IPv6 block for APNIC members with existing IPv4 space 5.1.1 Criteria 5.1.2 Minimum size of IPv6 block 5.2 Initial allocation 5.2.1 Initial allocation criteria 5.2.2 Minimum initial allocation size 5.2.3 Larger initial allocations 5.3 Subsequent allocation 5.3.1 Applied HD-Ratio 5.3.2 Alternative allocation criteria 5.3.3 Subsequent Allocation Size 5.4 LIR-to-ISP allocation 5.5 Assignment 5.5.1 Assignment address space size 5.5.2 Assignment of multiple /48s to a single end site 5.5.3 Assignment to operator's infrastructure 5.6 Registration 5.7 Reverse lookup 5.8 Existing IPv6 address space holders 5.9 Portable assignments 5.9.1 Small multihoming assignments 5.9.2 Internet Exchange Points 5.9.3 Critical infrastructure 6. References 7. Appendix A: HD-Ratio 8. Appendix B: Background information 8.1 Background 8.2 Why a joint policy 8.3 The size of IPv6's address space 8.4 Acknowledgment 1. Introduction 1.1 Overview This document describes policies for the allocation and assignment of globally-unique Internet Protocol Version 6 (IPv6) address space. It updates and obsoletes the existing Provisional IPv6 Policies in effect since 1999 [RIRv6-Policies]. Policies described in this document are intended to be adopted by each registry. However, adoption of this document does not preclude local variations in each region or area. [RFC2373, RFC2373bis] designate 2000::/3 to be global unicast address space that IANA may allocate to the RIRs. In accordance with [RFC2928, RFC2373bis, IAB-Request], IANA has allocated initial ranges of global unicast IPv6 address space from the 2001::/16 address block to the existing RIRs. This document concerns the initial and subsequent allocations of the 2000::/3 unicast address space, for which RIRs formulate allocation and assignment policies. This policy is considered to be an interim policy. It will be reviewed in the future, subject to greater experience in the administration of IPv6. 2. Definitions [note: some of these definitions will be replaced by definitions from other RIR documents in order to be more consistent.] The following terms and their definitions are of particular importance to the understanding of the goals, environment, and policies described in this document. Responsibility for management of IPv6 address spaces is distributed globally in accordance with the hierarchical structure shown below. Figure 1 Distribution Hierarchy +--------+ | IANA | +--------+ | +-----------+ | | +--------+ +--------+ | RIR | | RIR | Regional Internet +--------+ +--------+ Registries (APNIC, ARIN, RIPE NCC, | | plus possible future RIRs) | | | +-----+ | | NIR | National Internet | +-----+ Registries (AP region) | | +--------+ +--------+ |LIR/ISP | |LIR/ISP | Local Internet +--------+ +--------+ Registries (ISPs) | | +--------+ | | | | +-------+ +----+ +----+ |EU(ISP)| | EU | | EU | End users +-------+ +----+ +----+ 2.1 Internet Registry (IR) An Internet Registry (IR) is an organization that is responsible for distributing IP address space to its members or customers and for registering those distributions. IRs are classified according to their primary function and territorial scope within the hierarchical structure depicted in the figure above. 2.2 Regional Internet Registry (RIR) Regional Internet Registries (RIRs) are established and authorized by respective regional communities, and recognized by the IANA to serve and represent large geographical regions. The primary role of RIRs is to manage and distribute public Internet address space within their respective regions. 2.3 National Internet Registry (NIR) A National Internet Registry (NIR) primarily allocates address space to its members or constituents, which are generally LIRs organized at a national level. NIRs exist mostly in the Asia Pacific region. 2.4 Local Internet Registry (LIR) A Local Internet Registry (LIR) is an IR that primarily assigns address space to the users of the network services that it provides. LIRs are generally ISPs, whose customers are primarily end users and possibly other ISPs. 2.5 Allocate To allocate means to distribute address space to IRs for the purpose of subsequent distribution by them. 2.6 Assign To assign means to delegate address space to an ISP or end-user, for specific use within the Internet infrastructure they operate. Assignments must only be made for specific purposes documented by specific organizations and are not to be sub-assigned to other parties. 2.7 Utilization The actual usage of addresses within each assignment will be quite low, when compared to IPv4 assignments. In IPv6, "utilization" is only measured in terms of the bits to the left of the /56 boundary. In other words, utilization refers to the assignment of /56s to end sites, and not the number of addresses assigned within individual /56s at those end sites. Throughout this document, the term utilization refers to the allocation of /56s to end sites, and not the number of addresses assigned within individual /56s within those end sites. 2.8 HD-Ratio The HD-Ratio is a way of measuring the efficiency of address assignment [RFC 3194]. It is an adaptation of the H-Ratio originally defined in [RFC1715] and is expressed as follows: Log (number of allocated objects) HD = ------------------------------------------------ Log (maximum number of allocatable objects) where (in the case of this document) the objects are IPv6 site addresses (/56s) assigned from an IPv6 prefix of a given size. 2.9 End site An end site is defined as an end user (subscriber) who has a business relationship with a service provider that involves: * that service provider assigning address space to the end user * that service provider providing transit service for the end user to other sites * that service provider carrying the end user's traffic * that service provider advertising an aggregate prefix route that contains the end user's assignment 2.10 Internet Exchange Point (IXP) An Internet Exchange Point (IX or IXP) is a layer 1 and layer 2 network structure that interconnects three or more Autonomous Systems (AS) for the purpose of Internet traffic interchange. 3. Goals of IPv6 address space management 3.1 Goals IPv6 address space is a public resource that must be managed in a prudent manner with regards to the long-term interests of the internet. Responsible address space management involves balancing a set of sometimes competing goals. The following are the goals relevant to IPv6 address policy. 3.2 Uniqueness Every assignment and/or allocation of address space must guarantee uniqueness worldwide. This is an absolute requirement for ensuring that every public host on the Internet can be uniquely identified. 3.3 Registration Internet address space must be registered in a registry database accessible to appropriate members of the Internet community. This is necessary to ensure the uniqueness of each Internet address and to provide reference information for Internet troubleshooting at all levels, ranging from all RIRs and IRs to end users. The goal of registration should be applied within the context of reasonable privacy considerations and applicable laws. 3.4 Aggregation Wherever possible, address space should be distributed in a hierarchical manner, according to the topology of network infrastructure. This is necessary to permit the aggregation of routing information by ISPs, and to limit the expansion of Internet routing tables. This goal is particularly important in IPv6 addressing, where the size of the total address pool creates significant implications for both internal and external routing. IPv6 address policies should seek to avoid fragmentation of address ranges. Further, RIRs should apply practices that maximize the potential for subsequent allocations to be made contiguous with past allocations currently held. However, there can be no guarantee of contiguous allocation. 3.5 Conservation Although IPv6 provides an extremely large pool of address space, address policies should avoid unnecessarily wasteful practices. Requests for address space should be supported by appropriate documentation and stockpiling of unused addresses should be avoided. 3.6 Fairness All policies and practices relating to the use of public address space should apply fairly and equitably to all existing and potential members of the Internet community, regardless of their location, nationality, size or any other factor. 3.7 Minimized Overhead It is desirable to minimize the overhead associated with obtaining address space. Overhead includes the need to go back to RIRs for additional space too frequently, the overhead associated with managing address space that grows through a number of small successive incremental expansions rather than through fewer, but larger, expansions. 3.8 Conflict of goals The goals described above will often conflict with each other, or with the needs of individual IRs or end users. All IRs evaluating requests for allocations and assignments must make judgments, seeking to balance the needs of the applicant with the needs of the Internet community as a whole. In IPv6 address policy, the goal of aggregation is considered to be the most important. 4. IPv6 Policy Principles To address the goals described in the previous section, the policies in this document discuss and follow the basic principles described below. 4.1 Address space not to be considered property It is contrary to the goals of this document and is not in the interests of the Internet community as a whole for address space to be considered freehold property. The policies in this document are based upon the understanding that globally-unique IPv6 unicast address space is licensed for use rather than owned. Specifically, IP addresses will be allocated and assigned on a license basis, with licenses subject to renewal on a periodic basis. The granting of a license is subject to specific conditions applied at the start or renewal of the license. RIRs will generally renew licenses automatically, provided requesting organizations are making a good-faith effort at meeting the criteria under which they qualified for or were granted an allocation or assignment. However, in those cases where a requesting organization is not using the address space as intended, or is showing bad faith in following through on the associated obligation, RIRs reserve the right to not renew the license. Note that when a license is renewed, the new license will be evaluated under and governed by the applicable IPv6 address policies in place at the time of renewal, which may differ from the policy in place at the time of the original allocation or assignment. 4.2 Routability not guaranteed There is no guarantee that any address allocation or assignment will be globally routable. However, RIRs must apply procedures that reduce the possibility of fragmented address space which may lead to a loss of routability. 4.3 Minimum Allocation RIRs will apply a minimum size for IPv6 allocations, to facilitate prefix-based filtering. The minimum allocation size for IPv6 address space is /32. 4.4 Consideration of IPv4 infrastructure Subject to section 5.2.3, existing IPv4 networks may be considered in determining the initial IPv6 allocation size. 5. Policies for allocations and assignments 5.1 Initial IPv6 block for APNIC members with existing IPv4 space 5.1.1 Criteria APNIC members that have received an IPv4 address block from APNIC but have no IPv6 space can qualify for an appropriately sized IPv6 block under the matching IPv6 policy. For example, a member that has received an IPv4 IXP assignment will be eligible to receive an IPv6 IXP assignment. 5.1.2 Minimum size of IPv6 block The size of the IPv6 delegation for members that meet this criteria will be based on the following: * A member that has an IPv4 allocation is eligible for a /32 IPv6 address block. * A member that has an IPv4 assignment is eligible for a /48 IPv6 address block. If an APNIC member wishes to receive an initial allocation or assignment larger than the sizes described above, the member will need to apply under the alternative criteria described in sections 5.2 and 5.5 below. 5.2 Initial allocation 5.2.1 Initial allocation criteria To qualify for an initial allocation of IPv6 address space, an organization must: a. Be an LIR b. Not be an end site c. Plan to provide IPv6 connectivity to organizations to which it will make assignments. d. Meet one of the two following criteria: * Have a plan for making at least 200 assignments to other organizations within two years OR * Be an existing LIR with IPv4 allocations from an APNIC or an NIR, which will make IPv6 assignments or sub-allocations to other organizations and announce the allocation in the inter- domain routing system within two years Private networks (those not connected to the public Internet) may also be eligible for an IPv6 address space allocation provided they meet equivalent criteria to those listed above. 5.2.2 Minimum initial allocation size Organizations that meet the initial allocation criteria are eligible to receive a minimum allocation of /32. 5.2.3 Larger initial allocations Initial allocations larger than /32 may be justified if: 1. The organization provides comprehensive documentation of planned IPv6 infrastructure which would require a larger allocation; or 2. The organization provides comprehensive documentation of all of the following: * its existing IPv4 infrastructure and customer base, * its intention to provide its existing IPv4 services via IPv6, and * its intention to move some of its existing IPv4 customers to IPv6 within two years. In either case, an allocation will be made which fulfills the calculated address requirement, in accordance with the HD-Ratio based utilization policy. 5.3 Subsequent allocation Organizations that hold an existing IPv6 allocation may receive a subsequent allocation in accordance with the following policies. 5.3.1 Applied HD-Ratio Subsequent allocation will be provided when an organization (ISP/LIR) satisfies the evaluation threshold of past address utilization in terms of the number of sites in units of /56 assignments. The HD- Ratio [RFC 3194] is used to determine the utilization thresholds that justify the allocation of additional address as described below. The HD-Ratio value of 0.94 is adopted as indicating an acceptable address utilization for justifying the allocation of additional address space. Appendix A provides a table showing the number of assignments that are necessary to achieve an acceptable utilization value for a given address block size. 5.3.2 Alternative allocation criteria Alternatively, a subsequent allocation may be provided where an organization (ISP/LIR) can demonstrate a valid reason for requiring the subsequent allocation. For guidelines on what will be considered a valid technical or other reason, see “APNIC guidelines for IPv6 allocation and assignment requests”. http://www.apnic.net/criteria/ipv6-guidelines 5.3.3 Subsequent Allocation Size When an organization has achieved an acceptable utilization for its allocated address space, it is immediately eligible to obtain an additional allocation that results in a doubling of the address space allocated to it. Where possible, except where separate disaggregated ranges are requested for multiple discreet networks, the allocation will be made from an adjacent address block, meaning that its existing allocation is extended by one bit to the left. If an organization needs more address space, it must provide documentation justifying its requirements for a two-year period. The allocation made will be based on this requirement. 5.4 LIR-to-ISP allocation There is no specific policy for an organization (LIR) to allocate address space to subordinate ISPs. Each LIR organization may develop its own policy for subordinate ISPs to encourage optimum utilization of the total address block allocated to the LIR. However, all /48 assignments to end sites are required to be registered either by the LIR or its subordinate ISPs in such a way that the RIR/NIR can properly evaluate the HD-Ratio when a subsequent allocation becomes necessary. 5.5 Assignment LIRs must make IPv6 assignments in accordance with the following provisions. 5.5.1 Assignment address space size End-users are assigned an end site assignment from their LIR or ISP. The exact size of the assignment is a local decision for the LIR or ISP to make, using a minimum value of a /64 (when only one subnet is anticipated for the end site) up to the normal maximum of /48, except in cases of extra large end sites where a larger assignment can be justified. RIRs/NIRs are not concerned about which address size an LIR/ISP actually assigns. Accordingly, RIRs/NIRs will not request the detailed information on IPv6 user networks as they did in IPv4, except for the cases described in Section 4.4 and for the purposes of measuring utilization as defined in this document. 5.5.2 Assignment of multiple /48s to a single end site When a single end site requires an additional /48 address block, it must request the assignment with documentation or materials that justify the request. Requests for multiple or additional /48s will be processed and reviewed (i.e., evaluation of justification) at the RIR/NIR level. Note: There is no experience at the present time with the assignment of multiple /48s to the same end site. Having the RIR review all such assignments is intended to be a temporary measure until some experience has been gained and some common policies can be developed. In addition, additional work at defining policies in this space will likely be carried out in the near future. 5.5.3 Assignment to operator's infrastructure An organization (ISP/LIR) may assign a /48 per PoP as the service infrastructure of an IPv6 service operator. Each assignment to a PoP is regarded as one assignment regardless of the number of users using the PoP. A separate assignment can be obtained for the in-house operations of the operator. 5.6 Registration When an organization holding an IPv6 address allocation makes IPv6 address assignments, it must register assignment information in a database, accessible by RIRs as appropriate (information registered by an RIR/NIR may be replaced by a distributed database for registering address management information in future). Information is registered in units of assigned /48 networks. When more than a /48 is assigned to an organization, the assigning organization is responsible for ensuring that the address space is registered in an RIR/NIR database. RIR/NIRs will use registered data to calculate the HD-Ratio at the time of application for subsequent allocation and to check for changes in assignments over time. IRs shall maintain systems and practices that protect the security of personal and commercial information that is used in request evaluation, but which is not required for public registration. Organizations that receive an allocation from APNIC can choose whether or not their customer assignment registrations should be publicly available. If the organization does not indicate a choice, or it chooses to hide its customer assignment registrations, then those records will not be visible in the public whois database. Whois queries on these records will return details of the allocation. In addition, it is mandatory to register an Incident Report Team (IRT) object for each allocation and assignment record in the APNIC Whois Database. 5.7 Reverse lookup When an RIR/NIR delegates IPv6 address space to an organization, it also delegates the responsibility to manage the reverse lookup zone that corresponds to the allocated IPv6 address space. Each organization should properly manage its reverse lookup zone. When making an address assignment, the organization must delegate to an assignee organization, upon request, the responsibility to manage the reverse lookup zone that corresponds to the assigned address. 5.8 Existing IPv6 address space holders Organizations that received /35 IPv6 allocations under the previous IPv6 address policy [RIRv6-Policies] are immediately entitled to have their allocation expanded to a /32 address block, without providing justification, so long as they satisfy the criteria in Section 5.1.1. The /32 address block will contain the already allocated smaller address block (one or multiple /35 address blocks in many cases) that was already reserved by the RIR for a subsequent allocation to the organization. Requests for additional space beyond the minimum /32 size will be evaluated as discussed elsewhere in the document. 5.9 Portable assignments 5.9.1 Small multihoming assignments An organization is eligible to receive a portable assignment from APNIC if it is currently multihomed or plans to be multihomed within three months. An organization is considered to be multihomed if its network receives full-time connectivity from more than one ISP and has one or more routing prefixes announced by at least two of its ISPs. The minimum assignment made under these terms is /48. Address space assigned under these terms and not used for multihoming three months after assignment by APNIC will be reclaimed. 5.9.2 Internet Exchange Points Internet Exchange Points are eligible to receive a portable assignment from APNIC to be used exclusively to connect the IXP participant devices to the Exchange Point. The minimum assignment made under these terms is /48. Global routability of the portable assignment is left to the discretion of the IXP and its participants. 5.9.3 Critical infrastructure The following critical infrastructure networks, if operating in the Asia Pacific region, are eligible to receive a portable assignment: * root domain name system (DNS) server; * global top level domain (gTLD) nameservers; * country code TLD (ccTLDs) nameservers; * IANA; * Regional Internet Registry (RIRs); and * National Internet Registry (NIRs). Assignments to critical infrastructure are available only to the actual operators of the network infrastructure performing such functions. Registrar organizations which do not actually host the network housing the registry infrastructure, will not be eligible for an assignment under this policy. The maximum assignment made under these terms is /32 per operator. Exchanges made under this policy remain subject to the address space license policy. 6. References [RFC1715] "The H Ratio for Address Assignment Efficiency", C. Huitema. November 1994, RFC 1715. [IAB-Request] "Email from IAB to IANA", http://www.iab.org/iab/DOCUMENTS/IPv6addressspace.txt. [RFC2373] "IP Version 6 Addressing Architecture", R. Hinden, S. Deering. July 1998, RFC 2373. [RFC2373bis] draft-ietf-ipngwg-addr-arch-v3-07.txt. [RFC2928] "Initial IPv6 Sub-TLA ID Assignments", R. Hinden, S. Deering, R. Fink, T. Hain. September 2000, RFC 2928. [RFC3177] "IAB/IESG Recommendations on IPv6 Address". IAB, IESG. September 2001, RFC 3177. [RFC3194] "The H-Density Ratio for Address Assignment Efficiency An Update on the H ratio", A. Durand, C. Huitema. November 2001, RFC 3194. [RIRs-on-48] http://www.arin.net/library/guidelines/ipv6_initial.html, [RIRv6-Policies] http://www.arin.net/regserv/ipv6/ipv6guidelines.html, http://www.ripe.net/ripe/docs/ripe-196.html, http://archive.apnic.net/docs/drafts/ipv6/ipv6-policy-280599.html. 7. Appendix A: HD-Ratio The utilization threshold T, expressed as a number of individual /56 prefixes to be allocated from IPv6 prefix P, can be calculated as: T=2((56-P)*HD) Thus, the utilization threshold for an organization requesting subsequent allocation of IPv6 address block is specified as a function of the prefix size and target HD ratio. This utilization refers to the allocation of /56s to end sites, and not the utilization of those /56s within those end sites. It is an address allocation utilization ratio and not an address assignment utilization ratio. This document adopts an HD-Ratio of 0.94 as the utilization threshold for IPv6 address space allocations. The following table provides equivalent absolute and percentage address utilization figures for IPv6 prefixes, corresponding to an HD-Ratio of 0.94 P 56-P Total /56s Threshold Util % 56 0 1 1 100.0 55 1 2 2 95.9 54 2 4 4 92.0 53 3 8 7 88.3 52 4 16 14 84.7 51 5 32 26 81.2 50 6 64 50 77.9 49 7 128 96 74.7 48 8 256 184 71.7 47 9 512 352 68.8 46 10 1,024 676 66.0 45 11 2,048 1,296 63.3 44 12 4,096 2,487 60.7 43 13 8,192 4,771 58.2 42 14 16,384 9,153 55.9 41 15 32,768 17,560 53.6 40 16 65,536 33,689 51.4 39 17 131,072 64,634 49.3 38 18 262,144 124,002 47.3 37 19 524,288 237,901 45.4 36 20 1,048,576 456,419 43.5 35 21 2,097,152 875,653 41.8 34 22 4,194,304 1,679,965 40.1 33 23 8,388,608 3,223,061 38.4 32 24 16,777,216 6,183,533 36.9 31 25 33,554,432 11,863,283 35.4 30 26 67,108,864 22,760,044 33.9 29 27 134,217,728 43,665,787 32.5 28 28 268,435,456 83,774,045 31.2 27 29 536,870,912 160,722,871 29.9 26 30 1,073,741,824 308,351,367 28.7 25 31 2,147,483,648 591,580,804 27.5 24 32 4,294,967,296 1,134,964,479 26.4 23 33 8,589,934,592 2,177,461,403 25.3 22 34 17,179,869,184 4,177,521,189 24.3 21 35 34,359,738,368 8,014,692,369 23.3 20 36 68,719,476,736 15,376,413,635 22.4 19 37 137,438,953,472 29,500,083,768 21.5 18 38 274,877,906,944 56,596,743,751 20.6 17 39 549,755,813,888 108,582,451,102 19.8 16 40 1,099,511,627,776 208,318,498,661 18.9 15 41 2,199,023,255,552 399,664,922,315 18.2 14 42 4,398,046,511,104 766,768,439,460 17.4 13 43 8,796,093,022,208 1,471,066,903,609 16.7 12 44 17,592,186,044,416 2,822,283,395,519 16.0 11 45 35,184,372,088,832 5,414,630,391,777 15.4 10 46 70,368,744,177,664 10,388,121,308,479 14.8 9 47 140,737,488,355,328 19,929,904,076,845 14.2 8 48 281,474,976,710,656 38,236,083,765,023 13.6 7 49 562,949,953,421,312 73,357,006,438,603 13.0 6 50 1,125,899,906,842,620 140,737,488,355,328 12.5 5 51 2,251,799,813,685,250 270,008,845,646,446 12.0 4 52 4,503,599,627,370,500 518,019,595,058,136 11.5 8. Appendix B: Background information 8.1 Background The impetus for revising the 1999 Provisional IPv6 policy started with the APNIC meeting held in Taiwan in August 2001. Follow-on discussions were held at the October, 2001 RIPE and ARIN meetings. During these meetings, the participants recognized an urgent need for more detailed, complete policies. One result of the meetings was the establishment of a single mailing list to discuss a revised policy together with a desire to develop a general policy that all RIRs could use. This document does not provide details of individual discussions that lead to policies described in this document; detailed information can be found in the individual meeting minutes at the www.apnic.net, www.arin.net, and www.ripe.net web sites. 8.2 Why a joint policy IPv6 addresses are a public resource that must be managed with consideration to the long-term interests of the internet community. Although regional registries adopt allocation policies according to their own internal processes, address policies should largely be uniform across registries. Having significantly varying policies in different regions is undesirable because it can lead to situations where "registry shopping" can occur as requesting organizations request addresses from the registry that has the most favorable policy for their particular desires. This can lead to the policies in one region undermining the efforts of registries in other regions with regards to prudent stewardship of the address space. In cases where regional variations from the policy are deemed necessary, the preferred approach is to raise the issue in the other regional registries in order to develop a consensus approach that all registries can support. 8.3 The size of IPv6's address space It should be noted that the 128-bit address space is divided into three logical parts, with the usage of each component managed differently. The rightmost 64 bits, the Interface Identifier [RFC2373], will often be a globally-unique IEEE identifier (e.g., mac address). Although an "inefficient" way to use the Interface Identifier field from the perspective of maximizing the number of addressable nodes, the numbering scheme was explicitly chosen to simplify Stateless Address Autoconfiguration [RFC2462]. The middle bits of an address indicate the subnet ID. 8.4 Acknowledgment The initial version of this document was produced by The JPNIC IPv6 policy drafting team consisting of Akihiro Inomata, Akinori Maemura, Kosuke Ito, Kuniaki Kondo, Takashi Arano, Tomohiro Fujisaki, and Toshiyuki Yamasaki. Special thanks goes out to this team, who worked over a holiday in order to produce an initial document quickly. An editing team was then organized by representatives from each of the three RIRs (Takashi Arano, Chair of APNIC's Policy SIG, Thomas Narten, Chair of ARIN's IPv6 WG, and David Kessens, Chair of RIPE NCC's IPv6 WG). The editing team would like to acknowledge the contributions to this document of Takashi Arano, John Crain, Steve Deering, Gert Doering, Kosuke Ito, Richard Jimmerson, David Kessens, Mirjam Kuehne, Anne Lord, Jun Murai, Paul Mylotte, Thomas Narten, Ray Plzak, Dave Pratt, Stuart Prevost, Barbara Roseman, Gerard Ross, Paul Wilson, Cathy Wittbrodt and Wilfried Woeber. The final editing of the initial document was done by Thomas Narten.