Unified IPv4-in-IPv6 Softwire Customer Premises Equipment (CPE): A DHCPv6-Based Prioritization Mechanism
RFC 8026

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Internet Engineering Task Force (IETF)                      M. Boucadair
Request for Comments: 8026                                        Orange
Category: Standards Track                                      I. Farrer
ISSN: 2070-1721                                      Deutsche Telekom AG
                                                           November 2016

    Unified IPv4-in-IPv6 Softwire Customer Premises Equipment (CPE):
                A DHCPv6-Based Prioritization Mechanism

Abstract

   In IPv6-only provider networks, transporting IPv4 packets
   encapsulated in IPv6 is a common solution to the problem of IPv4
   service continuity.  A number of differing functional approaches have
   been developed for this, each having their own specific
   characteristics.  As these approaches share a similar functional
   architecture and use the same data plane mechanisms, this memo
   specifies a DHCPv6 option, whereby a single instance of Customer
   Premises Equipment (CPE) can interwork with all of the standardized
   and proposed approaches to providing encapsulated IPv4-in-IPv6
   services by providing a prioritization mechanism.

Status of This Memo

   This is an Internet Standards Track document.

   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
   Internet Standards is available in Section 2 of RFC 7841.

   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/rfc8026.

Boucadair & Farrer           Standards Track                    [Page 1]
RFC 8026            OPTION_S46_PRIORITY DHCPv6 Option      November 2016

Copyright Notice

   Copyright (c) 2016 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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
       1.1.1.  Requirements Language . . . . . . . . . . . . . . . .   4
     1.2.  Rationale . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  DHCPv6 S46 Priority Option  . . . . . . . . . . . . . . .   5
     1.4.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . . . .   6
     1.5.  DHCPv6 Server Behavior  . . . . . . . . . . . . . . . . .   7
   2.  Operator Deployment Considerations for Deploying Multiple
       Softwire Mechanisms . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Client Address Planning . . . . . . . . . . . . . . . . .   7
     2.2.  Backwards Compatability with Existing Softwire Clients  .   7
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  S46 Mechanisms and Their Identifying Option Codes . . . .   8
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

Boucadair & Farrer           Standards Track                    [Page 2]
RFC 8026            OPTION_S46_PRIORITY DHCPv6 Option      November 2016

1.  Introduction

   IPv4 service continuity is one of the major technical challenges that
   must be considered during IPv6 migration.  Over the past few years, a
   number of different approaches have been developed to assist with
   this problem (e.g., as described in [RFC6333], [RFC7596], and
   [RFC7597]).  These approaches, referred to as "S46 mechanisms" in
   this document, exist in order to meet the particular deployment,
   scaling, addressing, and other requirements of different service
   providers' networks.

   A common feature shared among all of the differing modes is the
   integration of softwire tunnel endpoint functionality into the
   Customer Premises Equipment (CPE) router.  Due to this inherent data
   plane similarity, a single CPE may be capable of supporting several
   different approaches.  Users may also wish to configure a specific