IPv4 Run-Out and IPv4-IPv6 Co-Existence Scenarios
RFC 6127

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Internet Engineering Task Force (IETF)                          J. Arkko
Request for Comments: 6127                                      Ericsson
Category: Informational                                      M. Townsley
ISSN: 2070-1721                                                    Cisco
                                                                May 2011

           IPv4 Run-Out and IPv4-IPv6 Co-Existence Scenarios

Abstract

   When IPv6 was designed, it was expected that the transition from IPv4
   to IPv6 would occur more smoothly and expeditiously than experience
   has revealed.  The growth of the IPv4 Internet and predicted
   depletion of the free pool of IPv4 address blocks on a foreseeable
   horizon has highlighted an urgent need to revisit IPv6 deployment
   models.  This document provides an overview of deployment scenarios
   with the goal of helping to understand what types of additional tools
   the industry needs to assist in IPv4 and IPv6 co-existence and
   transition.

   This document was originally created as input to the Montreal co-
   existence interim meeting in October 2008, which led to the
   rechartering of the Behave and Softwire working groups to take on new
   IPv4 and IPv6 co-existence work.  This document is published as a
   historical record of the thinking at the time, but hopefully will
   also help readers understand the rationale behind current IETF tools
   for co-existence and transition.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc6127.

Arkko & Townsley              Informational                     [Page 1]
RFC 6127               IPv4 and IPv6 Co-Existence               May 2011

Copyright Notice

   Copyright (c) 2011 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 ....................................................2
   2. Scenarios .......................................................4
      2.1. Reaching the IPv4 Internet .................................4
           2.1.1. NAT444 ..............................................5
           2.1.2. Distributed NAT .....................................6
           2.1.3. Recommendation ......................................8
      2.2. Running Out of IPv4 Private Address Space ..................9
      2.3. Enterprise IPv6-Only Networks .............................11
      2.4. Reaching Private IPv4-Only Servers ........................13
      2.5. Reaching IPv6-Only Servers ................................14
   3. Security Considerations ........................................16
   4. Conclusions ....................................................16
   5. References .....................................................17
      5.1. Normative References ......................................17
      5.2. Informative References ....................................17
   Appendix A. Acknowledgments .......................................20

1.  Introduction

   This document was originally created as input to the Montreal
   co-existence interim meeting in October 2008, which led to the
   rechartering of the Behave and Softwire working groups to take on new
   IPv4 and IPv6 co-existence work.  This document is published as a
   historical record of the thinking at the time, but hopefully will
   also help readers understand the rationale behind current IETF tools
   for co-existence and transition.

Arkko & Townsley              Informational                     [Page 2]
RFC 6127               IPv4 and IPv6 Co-Existence               May 2011

   When IPv6 was designed, it was expected that IPv6 would be enabled,
   in part or in whole, while continuing to run IPv4 side-by-side on the
   same network nodes and hosts.  This method of transition is referred