rfc1366.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 1366     Guidelines for Management of IP Address Space  October 1992


      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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RFC 1366     Guidelines for Management of IP Address Space  October 1992


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: [phone]
   EMail: [e-mail]































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