Basic Transition Mechanisms for IPv6 Hosts and Routers
RFC 4213

Network Working Group                                        E. Nordmark
Request for Comments: 4213                        Sun Microsystems, Inc.
Obsoletes: 2893                                              R. Gilligan
Category: Standards Track                                 Intransa, Inc.
                                                            October 2005

         Basic Transition Mechanisms for IPv6 Hosts and Routers

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies IPv4 compatibility mechanisms that can be
   implemented by IPv6 hosts and routers.  Two mechanisms are specified,
   dual stack and configured tunneling.  Dual stack implies providing
   complete implementations of both versions of the Internet Protocol
   (IPv4 and IPv6), and configured tunneling provides a means to carry
   IPv6 packets over unmodified IPv4 routing infrastructures.

   This document obsoletes RFC 2893.

Nordmark & Gilligan         Standards Track                     [Page 1]
RFC 4213            Basic IPv6 Transition Mechanisms        October 2005

Table of Contents

   1. Introduction ....................................................2
      1.1. Terminology ................................................3
   2. Dual IP Layer Operation .........................................4
      2.1. Address Configuration ......................................5
      2.2. DNS ........................................................5
   3. Configured Tunneling Mechanisms .................................6
      3.1. Encapsulation ..............................................7
      3.2. Tunnel MTU and Fragmentation ...............................8
           3.2.1. Static Tunnel MTU ...................................9
           3.2.2. Dynamic Tunnel MTU ..................................9
      3.3. Hop Limit .................................................11
      3.4. Handling ICMPv4 Errors ....................................11
      3.5. IPv4 Header Construction ..................................13
      3.6. Decapsulation .............................................14
      3.7. Link-Local Addresses ......................................17
      3.8. Neighbor Discovery over Tunnels ...........................18
   4. Threat Related to Source Address Spoofing ......................18
   5. Security Considerations ........................................19
   6. Acknowledgements ...............................................21
   7. References .....................................................21
      7.1. Normative References ......................................21
      7.2. Informative References ....................................21
   8. Changes from RFC 2893 ..........................................23

1.  Introduction

   The key to a successful IPv6 transition is compatibility with the
   large installed base of IPv4 hosts and routers.  Maintaining
   compatibility with IPv4 while deploying IPv6 will streamline the task
   of transitioning the Internet to IPv6.  This specification defines
   two mechanisms that IPv6 hosts and routers may implement in order to
   be compatible with IPv4 hosts and routers.

   The mechanisms in this document are designed to be employed by IPv6
   hosts and routers that need to interoperate with IPv4 hosts and
   utilize IPv4 routing infrastructures.  We expect that most nodes in
   the Internet will need such compatibility for a long time to come,
   and perhaps even indefinitely.

   The mechanisms specified here are:

   -  Dual IP layer (also known as dual stack):  A technique for
      providing complete support for both Internet protocols -- IPv4 and
      IPv6 -- in hosts and routers.

Nordmark & Gilligan         Standards Track                     [Page 2]
RFC 4213            Basic IPv6 Transition Mechanisms        October 2005

   -  Configured tunneling of IPv6 over IPv4:  A technique for
      establishing point-to-point tunnels by encapsulating IPv6 packets
      within IPv4 headers to carry them over IPv4 routing
      infrastructures.

   The mechanisms defined here are intended to be the core of a
   "transition toolbox" -- a growing collection of techniques that
   implementations and users may employ to ease the transition.  The
   tools may be used as needed.  Implementations and sites decide which