rfc1466.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.


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.




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   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:







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           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



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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.



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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: [phone]
   EMail: [e-mail]


































Gerich                                                         [Page 10]