Network 10 Considered Harmful (Some Practices Shouldn't be Codified)
RFC 1627

Document Type RFC - Informational (July 1994; No errata)
Obsoleted by RFC 1918
Last updated 2013-03-02
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Network Working Group                                            E. Lear
Request for Comments: 1627                        Silicon Graphics, Inc.
Category: Informational                                          E. Fair
                                                    Apple Computer, Inc.
                                                              D. Crocker
                                                  Silicon Graphics, Inc.
                                                              T. Kessler
                                                  Sun Microsystems, Inc.
                                                               July 1994

                     Network 10 Considered Harmful
                 (Some Practices Shouldn't be Codified)

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.


   Re-use of Internet addresses for private IP networks is the topic of
   the recent RFC 1597 [1].  It reserves a set of IP network numbers,
   for (re-)use by any number of organizations, so long as those
   networks are not routed outside any single, private IP network.  RFC
   1597 departs from the basic architectural rule that IP addresses must
   be globally unique, and it does so without having had the benefit of
   the usual, public review and approval by the IETF or IAB.  This
   document restates the arguments for maintaining a unique address
   space.  Concerns for Internet architecture and operations, as well as
   IETF procedure, are explored.


   Growth in use of Internet technology and in attachments to the
   Internet have taken us to the point that we now are in danger of
   running out of unassigned IP network numbers.  Initially, numbers
   were formally assigned only when a network was about to be attached
   to the Internet.  This caused difficulties when initial use of IP
   substantially preceded the decision and permission to attach to the
   Internet.  In particular, re-numbering was painful.  The lesson that
   we learned was that every IP address ought to be globally unique,
   independent of its attachment to the Internet.  This makes it
   possible for any two network entities to communicate, no matter where
   either might be located.  This model is the result of a decades-long
   evolution, through which the community realized how painful it can be
   to convert a network of computers to use an assigned number after

Lear, Fair, Crocker & Kessler                                   [Page 1]
RFC 1627             Network 10 Considered Harmful             July 1994

   using random or default addresses found on computers just out of the
   box.  RFC 1597 abrogates this model without benefit of general IETF
   community discussion and consensus, leaving policy and operational
   questions unasked and unanswered.


   A common -- if not universal -- ideal for the future of IP is for
   every system to be globally accessible, given the proper security
   mechanisms.  Whether such systems comprise toasters, light switches,
   utility power poles, field medical equipment, or the classic examples
   of "computers", our current model of assignment is to ensure that
   they can interoperate.

   In order for such a model to work there must exist a globally unique
   addressing system.  A common complaint throughout the community is
   that the existing security in host software does not allow for every
   (or even many) hosts in a corporate environment to have direct IP
   access.  When this problem is addressed through proper privacy and
   authentication standards, non-unique IP addresses will become a
   bottleneck to easy deployment if the recommendations in RFC 1597 are

   The IP version 4 (IPv4) address space will be exhausted.  The
   question is simply:  when?

   If we assert that all IP addresses must be unique globally, connected
   or not, then we will run out of IP address space soon.

   If we assert that only IP addresses used on the world-wide Internet
   need to be globally unique, then we will run out of IP address space

   It is absolutely key to keep the Internet community's attention
   focused on the efforts toward IP next generation (IPng), so that we
   may transcend the limitations of IPv4.  RFC 1597 produces apparent
   relief from IPv4 address space exhaustion by masking those networks
   that are not connecting to the Internet, today.  However, this
   apparent relief will likely produce two results: complacency on the
   large part of the community that does not take the long term view,
   and a very sudden IP address space exhaustion at some later date.

   Prior to IPng deployment, it is important to preserve all the
   semantics that make both the Internet and Internet technology so very
   valuable for interoperability.  Apple Computer, IBM, and Motorola
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