





Network Working Group                                          E. Gerich
Request for Comments: 1366                                         Merit
                                                            October 1992


             Guidelines for Management of IP Address Space

Status 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 Task Force
   (FEPG) on behalf of the Federal Networking Council (FNC), the co-
   chairs of the International 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", 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
   of RFC 1174 and which defines the allocation and assignment of the
   network number space.  There are three major topics to be addressed:

      1) Qualifications for Distributed Regional Registries

      2) Allocation of the Network Number Space by the Internet Registry



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      3) Assignment of the Network Numbers

2.0  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,
   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 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

      d) the commitment to allocate IP numbers according to
         the guidelines established by the IANA and the IR

      e) the commitment to coordinate with the IR to establish
         qualifications and strategies for sub-allocations of



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         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 subscribers 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 numbers; 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 (June 1992) [1]

   Class A and B network numbers are a limited resource and therefore
   the entire number space will be retained by the IR.  No allocations
   from the Class A and B network numbers will be made to distributed
   regional registries at this time.

   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.

   A preliminary 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.



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      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:

   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 subscribers has two major goals:



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      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 techniques

4.1  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 77 Class A
   network numbers which are unassigned, and these 77 network numbers
   represent about 30% of the total network number space.

   The IANA 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 new assignments of Class A
   numbers will take place in the near future, any organization
   petitioning the IANA 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 under utilization of
   the Class B number space by most organizations, the recommendation is
   now to use multiple Class Cs where practical.

   The IANA and the IR will maintain sole responsibility for the Class B
   number space.  Where there are designated regional registries, those
   registries will act in an auxiliary capacity in evaluating requests
   for Class B numbers.  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.

   These criteria assume that an organization which meets this profile
   will continue to grow and that assigning a Class B network number to
   them will permit network growth and reasonable utilization of the



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   assigned number space. There may be circumstances where it will be
   impossible to utilize a block of Class C network numbers in place of
   a Class B.  These situations will be considered on a case-by-case
   basis.

4.3  Class C

   Section 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 deals with how network numbers are assigned from within
   those blocks. 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 following criteria:

           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

   The number of addresses that a network subscriber indicates that it
   needs should be based on a 24 month projection.

   The maximal block of class C nets that should be assigned to a
   subscriber consists of sixteen contiguous class C networks which
   corresponds to a single IP prefix the length of which is twelve bits.
   If a subscriber has a requirement for more than 4096 unique IP
   addresses it should most likely receive a Class B net number.




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5.0  Conclusion

   This proliferation of class C network numbers may aid in preserving
   the scarcity 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 of
   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 International 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, 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 sighted for their comments.

7.0  References

   [1] 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.

   [2] "Internet Domain Survey", Network Information Systems Center, SRI
       International, July 1992.

   [3] Ford, P., "Working Draft - dated 6 May 1992", Work in Progress.

   [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. Varadha, "Supernetting: an
       Address Assignments and Aggregation Strategy", RFC 1338, BARRNet,
       cisco, Merit, OARnet, June 1992.




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   [6] Rekhter, Y., and T. Li, "Guidelines for IP Address Allocation",
       Work in Progress, August 1992.

   [7] Cerf, V., "IAB Recommended Policy on Distributing Internet
       Identifier Assignment and IAB Recommended Policy Change to
       Internet 'Connected' Status", RFC 1174, CNRI, August 1990.

Security Considerations

   Security issues are not discussed in this memo.

Author's Address

   Elise Gerich
   Merit Computer Network
   1075 Beal Avenue
   Ann Arbor, MI 48109-2112

   Phone: (313) 936-3000
   EMail: epg@MERIT.EDU































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