rfc1627.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

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.

SUMMARY

   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.

INTRODUCTION

   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



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   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.

KEEP OUR EYES ON THE PRIZE:  AN ARCHITECTURAL GOAL AND VIOLATION

   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
   followed.

   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
   later.

   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
   could not collaborate as easily as they have to produce the PowerPC
   without uniquely assigned IP addresses. The same can be said of the
   Silicon Graphics merger with MIPS. There are many, many more examples



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   that can be cited.

   It should be noted that a scheme similar to RFC 1597 can be
   implemented at the time that we actually run out of assignable IPv4
   address space; it simply requires that those organizations which have
   been assigned addresses but are not yet connected to the Internet
   return their addresses to IANA. It is important that the IAB (and
   IANA as its agent) reassert their ownership of the IP address space
   now, to preclude challenges to this type of reassignment.

OPERATIONAL ISSUES

RFC 1597 Implementations

   Methods are needed to ensure that the remaining addresses are
   allocated and used frugally.  Due to the current problems, Internet
   service providers have made it increasingly difficult for
   organizations to acquire public IP network numbers.  Private networks
   have always had the option of using addresses not assigned to them by
   appropriate authorities.  We do not know how many such networks
   exist, because by their nature they do not interact with the global
   Internet.  By using a random address, a company must take some care
   to ensure it is able to route to the properly registered owner of
   that network.

   RFC 1597 proposes to solve the routing problem by assigning numbers
   that will never be used outside of private environments.  Using such
   standard numbers introduces a potential for clashes in another way.
   If two private networks follow RFC 1597 and then later wish to
   communicate with each other, one will have to renumber.  The same
   problem occurs if a private network wishes to become public.  The
   likely cost of renumbering is linear to the number of hosts on a
   network.  Thus, a large company with 10,000 hosts on a network could
   incur considerable expense if it either merged with another company
   or joined the Internet in such a way as to allow all hosts to
   directly access the outside network.

   The probability of address clashes occurring over time approach 100%
   with RFC 1597.  Picking a random network number reduces the chances
   of having to renumber hosts, but introduces the routing problems
   described above.  Best of all, retrieving assigned numbers from the
   appropriate authority in the first place eliminates both existing and
   potential address conflicts at the cost of using a part of the
   address space.

   Apple Computer once believed that none of its internal systems would
   ever speak IP directly to the outside world, and as such, network
   operations picked IP class A network 90 out of thin air to use.



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RFC 1627             Network 10 Considered Harmful             July 1994


   Apple is only now recovering from this error, having renumbered some
   5,000 hosts to provide them with "desktop" Internet access.  Unless
   the Internet community reaffirms its commitment to a globally unique
   address space, we condemn many thousands of organizations to similar
   pain when they too attempt to answer the call of the global Internet.

   Another timely example of problems caused by RFC 1597 is Sun's use of
   Internet multicasting.  Sun selectively relays specific multicast
   conferences.  This has the effect of making many hosts at Sun visible
   to the Internet, even though they are not addressable via IP unicast
   routing.  If they had non-global addresses this would not work at
   all.  It is not possible to predict which machines need global
   addresses in advance.  Silicon Graphics has a similar configuration,
   as is likely for others, as well.

   Some might argue that assigning numbers to use for private networks
   will prevent accidental leaks from occurring through some sort of
   convention a'la Martian packets.  While the proposal attempts to
   create a standard for "private" address use, there is absolutely no
   way to ensure that other addresses are not also used.

   Hence, the "standard" becomes nothing but a misleading heuristic.  In
   fact, it is essential that routers to the global Internet advertise
   networks based only on explicit permission, rather than refusing to
   advertise others based on implicit prohibition, as supported by the
   policy formally created in RFC 1597.

Security Issues

   Administrators will have a hard time spotting unauthorized networks,
   when their network has been breached (either intentionally or
   unintentionally) because the other networks might have the same
   numbers as those normally in the routing tables.  More over, an
   inadvertent connection could possibly have a double whammy effect of
   partitioning two operational networks.

   It is worth emphasizing that IP providers should filter out all but
   authorized networks.  Such a practice would not only prevent
   accidents but also enhance the security of the Internet by reducing
   the potential number of points of attack.

   Internet multicasting adds a new dimension to security.  In some
   cases it may possible to allow multicasting through firewalls that
   completely restrict unicast routing.  Otherwise unconnected networks
   might well need unique addresses, as illustrated in the example
   above.





Lear, Fair, Crocker & Kessler                                   [Page 4]