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RFC 1466 - Guidelines for Management of IP Address Space


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Network Working Group                                          E. Gerich
Request for Comments: 1466                                         Merit
Obsoletes: 1366                                                 May 1993

             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 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
   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

      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, 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,

      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. (See section 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. (See
   section 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 addresses

   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:

   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 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 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 new

   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.

   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 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 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:

           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 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 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.

   [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.EDU

 

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