IANA-Reserved IPv4 Prefix for Shared Address Space
RFC 6598

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Internet Engineering Task Force (IETF)                           J. Weil
Request for Comments: 6598                             Time Warner Cable
BCP: 153                                                    V. Kuarsingh
Updates: 5735                                      Rogers Communications
Category: Best Current Practice                                C. Donley
ISSN: 2070-1721                                                CableLabs
                                                         C. Liljenstolpe
                                                           Telstra Corp.
                                                              M. Azinger
                                                 Frontier Communications
                                                              April 2012

           IANA-Reserved IPv4 Prefix for Shared Address Space

Abstract

   This document requests the allocation of an IPv4 /10 address block to
   be used as Shared Address Space to accommodate the needs of Carrier-
   Grade NAT (CGN) devices.  It is anticipated that Service Providers
   will use this Shared Address Space to number the interfaces that
   connect CGN devices to Customer Premises Equipment (CPE).

   Shared Address Space is distinct from RFC 1918 private address space
   because it is intended for use on Service Provider networks.
   However, it may be used in a manner similar to RFC 1918 private
   address space on routing equipment that is able to do address
   translation across router interfaces when the addresses are identical
   on two different interfaces.  Details are provided in the text of
   this document.

   This document details the allocation of an additional special-use
   IPv4 address block and updates RFC 5735.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   BCPs is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6598.

Weil, et al.              Best Current Practice                 [Page 1]
RFC 6598              Shared Address Space Request            April 2012

IESG Note

   A number of operators have expressed a need for the special-purpose
   IPv4 address allocation described by this document.  During
   deliberations, the IETF community demonstrated very rough consensus
   in favor of the allocation.

   While operational expedients, including the special-purpose address
   allocation described in this document, may help solve a short-term
   operational problem, the IESG and the IETF remain committed to the
   deployment of IPv6.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Requirements Language ...........................................3
   3. Alternatives to Shared Address Space ............................3
   4. Use of Shared CGN Space .........................................4
   5. Risk ............................................................5
      5.1. Analysis ...................................................5
      5.2. Empirical Data .............................................6
   6. Security Considerations .........................................7
   7. IANA Considerations .............................................8
   8. References ......................................................8
      8.1. Normative References .......................................8
      8.2. Informative References .....................................9
   Appendix A. Acknowledgments .......................................10

Weil, et al.              Best Current Practice                 [Page 2]
RFC 6598              Shared Address Space Request            April 2012

1.  Introduction

   IPv4 address space is nearly exhausted.  However, ISPs must continue
   to support IPv4 growth until IPv6 is fully deployed.  To that end,
   many ISPs will deploy a Carrier-Grade NAT (CGN) device, such as that