An Appeal to the Internet Community to Return Unused IP Networks (Prefixes) to the IANA
RFC 1917

Document Type RFC - Best Current Practice (February 1996; No errata)
Also known as BCP 4
Author Philip Nesser 
Last updated 2013-03-02
Stream Internet Engineering Task Force (IETF)
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Network Working Group                                       P. Nesser II
Request for Comments: 1917                    Nesser & Nesser Consulting
BCP: 4                                                     February 1996
Category: Best Current Practice

             An Appeal to the Internet Community to Return
               Unused IP Networks (Prefixes) to the IANA

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.


   This document is an appeal to the Internet community to return unused
   address space, i.e. any block of consecutive IP prefixes, to the
   Internet Assigned Numbers Authority (IANA) or any of the delegated
   registries, for reapportionment.  Similarly an appeal is issued to
   providers to return unused prefixes which fall outside their
   customary address blocks to the IANA for reapportionment.

1. Background

   The Internet of today is a dramatically different network than the
   original designers ever envisioned.  It is the largest public data
   network in the world, and continues to grow at an exponential rate
   which doubles all major operational parameters every nine months.  A
   common metaphor in engineering is that every time a problem increases
   in size by an order of magnitude, it becomes a new problem.  This
   adage has been true over the lifetime of the Internet.

   The Internet is currently faced with two major operational problems
   (amoung others).  The first is the eventual exhaustion of the IPv4
   address space and the second is the ability to route packets between
   the large number of individual networks that make up the Internet.
   The first problem is simply one of supply.  There are only 2^32 IPv4
   addresses available.  The lifetime of that space is proportional to
   the efficiency of its allocation and utilization.  The second problem
   is mainly a capacity problem.  If the number of routes exceeds the
   current capacity of the core Internet routers, some routes will be
   dropped and sections of the Internet will no longer be able to
   communicate with each other.  The two problems are coupled and the
   dominant one has, and will, change over time.

Nesser                   Best Current Practice                  [Page 1]
RFC 1917      Appeal to Return Unused IP Networks to IANA  February 1996

   The initial design of IP had all addresses the same, eight bits of
   network number and twenty four bits of host number.  The expectation
   was of a few, large, global networks.  During the first spurts of
   growth, especially with the invention of LAN technologies, it became
   obvious that this assumption was wrong and the separation of the
   address space into three classes (Class A for a few huge networks;
   Class B for more, smaller networks; and Class C for those really
   small LANs, with lots of network numbers) was implemented.  Soon
   subnets were added so sites with many small LANs could appear as a
   single network to others, the first step at limiting routing table
   size.  And finally, CIDR was introduced to the network, to add even
   more flexibility to the addressing, extending the split from three
   classes to potentially thirty different classes.

   Subnets were introduced to provide a mechanism for sites to divide a
   single network number (Class A, B, or C) into pieces, allowing a
   higher utilization of address space, and thus promoting conservation
   of the IPv4 address space.  Because of the built-in notion of
   classful addresses, subnetting automatically induced a reduction in
   the routing requirements on the Internet.  Instead of using two (or
   more) class C networks, a site could subnet a single class B into two
   (or more) subnets.  Both the allocation and the advertisement of a
   route to the second and succeeding class C's are saved.

   Since 1993, the concept of classless (the "C" in CIDR) addresses have
   been introduced to the Internet community.  Addresses are
   increasingly thought of as bitwise contiguous blocks of the entire
   address space, rather than a class A,B,C network.  For example, the
   address block formerly known as a Class A network, would be referred
   to as a network with a /8 prefix, meaning the first 8 bits of the
   address define the network portion of the address.  Sometimes the /8
   will be expressed as a mask of (in the same way a 16 bit
   subnet mask will be written as

   This scheme allows "supernetting" of addresses together into blocks
   which can be advertised as a single routing entry.  The practical
   purpose of this effort is to allow service providers and address
   registries to delegate realistic address spaces to organizations and
   be unfettered by the traditional network classes, which were
   inappropriately sized for most organizations.  For example the block
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