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Network Working Group                                          E. GerichRequest for Comments: 1466                                         MeritObsoletes:1366                                                 May 1993Guidelines for Management of IP Address SpaceStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard.  Distribution of this memo is   unlimited.Abstract   This document has been reviewed by the Federal Engineering Planning   Group (FEPG) on behalf of the Federal Networking Council (FNC), the   co-chairs of the Intercontinental Engineering Planning Group (IEPG),   and the Reseaux IP Europeens (RIPE).  There was general consensus by   those groups to support the recommendations proposed in this document   for management of the IP address space.1.0  Introduction   With the growth of the Internet and its increasing globalization,   much thought has been given to the evolution of the network number   allocation and assignment process.RFC 1174, "Identifier Assignment   and Connected Status", [1] dated August 1990 recommends that the   Internet Registry (IR) continue as the principal registry for network   numbers; however, the IR may allocate blocks of network numbers and   the assignment of those numbers to qualified organizations.  The IR   will serve as the default registry in cases where no delegated   registration authority has been identified.   The distribution of the registration function is desirable, and in   keeping with that goal, it is necessary to develop a plan which   manages the distribution of the network number space.  The demand for   network numbers has grown significantly within the last two years and   as a result the allocation of network numbers must be approached in a   more systematic fashion.   This document proposes a plan which will forward the implementation   ofRFC 1174 and which defines the allocation and assignment of the   network number space.  There are three major topics to be addressed:Gerich                                                          [Page 1]

RFC 1466     Guidelines for Management of IP Address Space      May 1993      1) Qualifications for Distributed Regional Registries      2) Allocation of the Network Number Space by the Internet Registry      3) Assignment of the Network Numbers2.0  Qualifications for Distributed Regional Registries   The major reason to distribute the registration function is that the   Internet serves a more diverse global population than it did at its   inception.  This means that registries which are located in distinct   geographic areas may be better able to serve the local community in   terms of language and local customs. While there appears to be wide   support for the concept of distribution of the registration function,   it is important to define how the candidate delegated registries will   be chosen and from which geographic areas.   Based on the growth and the maturity of the Internet in Europe, North   America, Central/South America and the Pacific Rim areas, it is   desirable to consider delegating the registration function to an   organization in each of those geographic areas.  Until an   organization is identified in those regions, the IR will continue to   serve as the default registry.  The IR remains the root registry and   continues to provide the registration function to all those regions   not covered by distributed regional registries.  And as other regions   of the world become more and more active in the Internet, the   Internet Assigned Numbers Authority (IANA) and the IR may choose to   look for candidate registries to serve the populations in those   geographic regions.   It is important that the regional registry is unbiased and and widely   recognized by network providers and subscribers within the geographic   region.  It is also important that there is just a single regional   registry per geographical region at this level to provide for   efficient and fair sub-allocation of the address space.  To be   selected as a distributed regional registry an organization should   meet the following criteria:      a) networking authorities within the geographic area         legitimize the organization,      b) the organization is well-established and has         legitimacy outside of the registry function,      c) the organization will commit appropriate resources to         provide stable, timely, and reliable service         to the geographic region,Gerich                                                          [Page 2]

RFC 1466     Guidelines for Management of IP Address Space      May 1993      d) is committed to allocate IP numbers according to         the guidelines established by the IANA and the IR, and      e) is committed to coordinate with the IR to establish         qualifications and strategies for sub-allocations of         the regional allocation.   The distributed regional registry is empowered by the IANA and the IR   to provide the network number registration function to a geographic   area.  It is possible for network applicants to contact the IR   directly.  Depending on the circumstances the network subscriber may   be referred to the regional registry, but the IR will be prepared to   service any network subscriber if necessary.3.0  Allocation of the Network Number Space by the Internet Registry   The Class A portion of the number space represents 50% of the total   IP host addresses; Class B is 25% of the total; Class C is   approximately 12% of the total.  Table 1 shows the current allocation   of the IP network numbers.                   Total           Allocated         Allocated (%)   Class A           126               49              38%   Class B         16383             7354              45%   Class C       2097151            44014               2%             Table 1: Network Number Statistics (May 1992) [2]   Class A and B network numbers are a limited resource and therefore   allocations from this space will be restricted.  The entire Class A   number space will be retained by the IANA and the IR.  No allocations   from the Class A network numbers will be made to distributed regional   registries at this time. (Seesection 4.1.)   Allocations from the Class B network number space will be restricted   also.  Small blocks of numbers may be allocated to regional   registries, which will be required to ensure that the allocation   guidelines are met. The IR will monitor those allocations. (Seesection 4.2.)   It is proposed that the IR, and any designated regional registries,   allocate addresses in conformance with this overall scheme. Where   there are qualifying regional registries established, primary   responsibility for allocation within that block will be delegated to   that registry. It should be noted that the Reseaux IP Europeens   Network Coordination Center (RIPE NCC) had been allocated a block of   Class C addresses (193.0.0 - 193.255.255) prior to the adoption of   this proposal. The RIPE NCC has agreed to allocate the addressesGerich                                                          [Page 3]

RFC 1466     Guidelines for Management of IP Address Space      May 1993   within that block according to the guidelines stated in this RFC.   The Class C network number space will be divided into allocatable   blocks which will be reserved by the IANA and IR for allocation to   distributed regional registries.  In the absence of designated   regional registries in geographic areas, the IR will assign addresses   to networks within those geographic areas according to the Class C   allocation divisions.   Inspection of the Class C IP network numbers shows that the number   space with prefixes 192 and 193 are assigned.  The remaining space   from prefix 194 through 223 is mostly unassigned.   The IANA and the IR will reserve the upper half of this space which   corresponds to the IP address range of 208.0.0.0 through   223.255.255.255. Network numbers from this portion of the Class C   space will remain unallocated and unassigned until further notice.   The remaining Class C network number space will be allocated in a   fashion which is compatible with potential address aggregation   techniques. It is intended to divide this address range into eight   equally sized address blocks.      192.0.0.0 - 193.255.255.255      194.0.0.0 - 195.255.255.255      196.0.0.0 - 197.255.255.255      198.0.0.0 - 199.255.255.255      200.0.0.0 - 201.255.255.255      202.0.0.0 - 203.255.255.255      204.0.0.0 - 205.255.255.255      206.0.0.0 - 207.255.255.255   Each block represents 131,072 addresses or approximately 6% of the   total Class C address space.   It is proposed that a broad geographic allocation be used for these   blocks.  At present there are four major areas of address allocation:   Europe, North America, Pacific Rim, and South & Central America.   In particular, the top level block allocation be designated as   follows:Gerich                                                          [Page 4]

RFC 1466     Guidelines for Management of IP Address Space      May 1993   Multi-regional          192.0.0.0 - 193.255.255.255   Europe                  194.0.0.0 - 195.255.255.255   Others                  196.0.0.0 - 197.255.255.255   North America           198.0.0.0 - 199.255.255.255   Central/South    America                200.0.0.0 - 201.255.255.255   Pacific Rim             202.0.0.0 - 203.255.255.255   Others                  204.0.0.0 - 205.255.255.255   Others                  206.0.0.0 - 207.255.255.255   It is proposed that the IR, and any designated regional registries,   allocate addresses in conformance with this overall scheme.  Where   there are qualifying regional registries established, primary   responsibility for allocation from within that block will be   delegated to that registry.   The ranges designated as "Others" permit flexibility in network   number assignments which are outside of the geographical regions   already allocated.  The range listed as multi-regional represents   network numbers which have been assigned prior to the implementation   of this plan.  It is proposed that the IANA and the IR will adopt   these divisions of the Class C network number space and will begin   assigning network numbers accordingly.4.0  Assignment of the Network Number Space   The exhaustion of the IP address space is a topic of concern for the   entire Internet community. This plan for the assignment of Class A,   B, or C IP numbers to network applicants has two major goals:      1) to reserve a portion of the IP number space so that it may be      available to transition to a new numbering plan      2) to assign the Class C network number space in a fashion which      is compatible with proposed address aggregation techniques4.1  Class A   The Class A number space can support the largest number of unique   host identifier addresses and is also the class of network numbers   most sparsely populated.  There are only approximately 11 Class A   network numbers which are unassigned or unreserved, and these 11   network numbers represent about 9% of the total address space.   The IANA and the IR will retain sole responsibility for the   assignment of Class A network numbers. The upper half of the Class A   number space will be reserved indefinitely (IP network addresses   64.0.0.0 through 127.0.0.0).  While it is expected that no newGerich                                                          [Page 5]

RFC 1466     Guidelines for Management of IP Address Space      May 1993   assignments of Class A numbers will take place in the near future,   any organization petitioning the IR for a Class A network number will   be expected to provide a detailed technical justification documenting   network size and structure. Class A assignments are at the IANA's   discretion.4.2  Class B   Previously, organizations were recommended to use a subnetted Class B   network number rather than multiple Class C network numbers.  Due to   the scarcity of Class B network numbers and the underutilization of   the Class B number space by most organizations, the recommendation is   now to use multiple Class Cs where practical.   The restrictions in allocation of Class B network numbers may cause   some organizations to expend additional resources to utilize multiple   Class C numbers. This is unfortunate, but inevitable if we implement   strategies to control the assignment of Class B addresses.  The   intent of these guidelines is to balance these costs for the greater   good of the Internet.4.2.1   Organizations applying for a Class B network number should fulfill   the following criteria:      1)  the organization presents a subnetting plan which documents          more than 32 subnets within its organizational network      AND      2)  the organization has more than 4096 hosts   Organizations applying for a Class B network number must submit an   engineering plan that documents its need for a Class B network   number.  This document must demonstrate that it is unreasonable to   engineer its network with a block of class C network numbers.  The   engineering plan must include how many hosts the network will have   within the next 24 months and how many hosts per subnet within the   next 24 months.   The submitted engineering plans will be held in strict confidence by   the Internet registries and will only be used to judge whether an   application is justified. If it is deemed that the applicant's   engineering plan, including the number of hosts and subnets, does not   warrant a Class B assignment, the applicant will be allocated a block   of Class C addresses.Gerich                                                          [Page 6]

RFC 1466     Guidelines for Management of IP Address Space      May 1993   There may be some circumstances where the organization is unable to   utilize a block of Class C network numbers and does not meet the   suggested criteria.  In such cases, the engineering plan should   clearly demonstrate their inability to utilize a block of Class C   network numbers.4.2.2   The IR may allocate small blocks of Class B network numbers to   regional registries if so doing will improve the service that is   being provided to the community.  The IR may issue more specific   guidelines for the further assignment of the numbers which will be   consistent with the stated guidelines.  The IR may require accounting   of the block assignment including receipt of the applicants'   engineering plans.  The IR may audit these engineering plans to   confirm that the assignments are consistent with the guidelines.4.3  Class CSection 3 of this document recommends a division of the Class C   number space.  That division is primarily an administrative division   which lays the groundwork for distributed network number registries.   This section addresses assignment of network numbers from within   regional block assignments. Sub-allocations of the block to sub-   registries is beyond the scope of this paper.   By default, if an organization requires more than a single Class C,   it will be assigned a bit-wise contiguous block from the Class C   space allocated for its geographic region.   For instance, an European organization which requires fewer than 2048   unique IP addresses and more than 1024 would be assigned 8 contiguous   class C network numbers from the number space reserved for European   networks, 194.0.0.0 - 195.255.255.255.  If an organization from   Central America required fewer than 512 unique IP addresses and more   than 256, it would receive 2 contiguous class C network numbers from   the number space reserved for Central/South American networks,   200.0.0.0 - 201.255.255.255.   The IR or the registry to whom the IR has delegated the registration   function will determine the number of Class C network numbers to   assign to a network subscriber based on the subscriber's 24 month   projection of required end system addresses according to the   following criteria:Gerich                                                          [Page 7]

RFC 1466     Guidelines for Management of IP Address Space      May 1993           Organization                            Assignment   1) requires fewer than 256 addresses    1 class C network   2) requires fewer than 512 addresses    2 contiguous class C networks   3) requires fewer than 1024 addresses   4 contiguous class C networks   4) requires fewer than 2048 addresses   8 contiguous class C networks   5) requires fewer than 4096 addresses  16 contiguous class C networks   6) requires fewer than 8192 addresses  32 contiguous class C networks   7) requires fewer than 16384 addresses 64 contiguous class C networks   If the subscriber's network is divided into logically distinct LANs   across which it would be difficult to use the given number of Class C   network numbers, the above criteria may apply on a per-LAN basis.   For example, if a subscriber has 600 hosts equally divided across ten   Ethernets, the allocation to that subscriber could be ten Class C   network numbers; one for each Ethernet. The subscriber would have to   support the request with to deviate from the stated criteria with an   engineering plan.   These criteria are not intended to cause a subscriber to subnet Class   C networks unneccessarily.  Although, if a subscriber has a small   number of hosts per subnet, the subscriber should investigate the   feasibility of subnetting Class C network numbers rather than   requesting one Class C network number for every subnet.  In cases   where the lack of Class C subnetting would result in an extravagant   waste of address space, the registries may request an engineering   plan detailing why subnetting is impossible.   If a subscriber has a requirement for more than 4096 unique IP   addresses it could conceivably receive a Class B network number.   However, there are cases where a subscriber may request a larger   block of Class C network numbers. For instance, if an organization   requires fewer than 8192 addresses and requests 32 Class C network   addresses, the regional registry may honor this request.  The maximal   block of Class C network numbers that should be assigned to a   subscriber consists of 64 contiguous Class C networks. This would   correspond to a single IP prefix of 18 bits.   Exceptions from the above stated criteria will be determined on a   case-by-case basis.5.0  Conclusion   This proliferation of class C network numbers may aid in retarding   the dispersion of class A and B numbers, but it is sure to accelerate   the explosion of routing information carried by Internet routers.   Inherent in these recommendations is the assumption that there will   be modifications in the technology to support the larger number ofGerich                                                          [Page 8]

RFC 1466     Guidelines for Management of IP Address Space      May 1993   network address assignments due to the decrease in assignments of   Class A and B numbers and the proliferation of Class C assignments.   Many proposals have been made to address the rapid growth of network   assignments and a discussion of those proposals is beyond the scope   and intent of this paper.   These recommendations for management of the current IP network number   space only profess to delay depletion of the IP address space, not to   postpone it indefinitely.6.0  Acknowledgements   The author would like to acknowledge the substantial contributions   made by the members of the following two groups, the Federal   Engineering Planning Group (FEPG) and the Intercontinental   Engineering Planning Group (IEPG). This document also reflects many   concepts expressed at the IETF Addressing BOF which took place in   Cambridge, MA in July 1992. In addition, Dan Long (BBN), Jon Postel   (ISI), and Yakov Rekhter (T.J. Watson Research Center, IBM Corp.)   reviewed this document and contributed to its content. The author   thanks those groups and individuals who have been cited for their   comments.7.0  References   [1] Cerf, V., "IAB Recommended Policy on Distributing Internet       Identifier Assignment and IAB Recommended Policy Change to       Internet 'Connected' Status",RFC 1174, CNRI, August 1990.   [2] Wang, Z., and J. Crowcroft, "A Two-Tier Address Structure for the       Internet: A Solution to the Problem of Address Space Exhaustion",RFC 1335, University College London, May 1992.Other related relevant work:   [3] "Internet Domain Survey", Network Information Systems Center, SRI       International, July 1992.   [4] Solensky, F., and F. Kastenholz, "A Revision to IP Address       Classifications", Work in Progress, March 1992.   [5] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Supernetting: an       Address Assignments and Aggregation Strategy",RFC 1338, BARRNet,       cisco, Merit, OARnet, June 1992.   [6] Rekhter, Y., and  Li, T.,"Guidelines for IP Address Allocation",       Work in Progress, August 1992.Gerich                                                          [Page 9]

RFC 1466     Guidelines for Management of IP Address Space      May 1993   [7] Rekhter, Y. and Topolcic, C., "Exchanging Routing Information       across Provider/Subscriber boundaries in CIDR environment", Work       in Progress, February 1993.8.0 Security Considerations   Security issues are not discussed in this memo.9.0 Author's Address   Elise Gerich   Merit Network, Inc.   1071 Beal Avenue   Ann Arbor, MI 48109-2112   Phone: (313) 936-3335   EMail: epg@MERIT.EDUGerich                                                         [Page 10]