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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RFC 1366     Guidelines for Management of IP Address Space  October 1992


     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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RFC 1366     Guidelines for Management of IP Address Space  October 1992


        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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RFC 1366     Guidelines for Management of IP Address Space  October 1992


  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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RFC 1366     Guidelines for Management of IP Address Space  October 1992


  [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: [email protected]































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