Default Address Selection for Internet Protocol Version 6 (IPv6)
RFC 6724

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Internet Engineering Task Force (IETF)                    D. Thaler, Ed.
Request for Comments: 6724                                     Microsoft
Obsoletes: 3484                                                R. Draves
Category: Standards Track                             Microsoft Research
ISSN: 2070-1721                                             A. Matsumoto
                                                                     NTT
                                                                T. Chown
                                               University of Southampton
                                                          September 2012

    Default Address Selection for Internet Protocol Version 6 (IPv6)

Abstract

   This document describes two algorithms, one for source address
   selection and one for destination address selection.  The algorithms
   specify default behavior for all Internet Protocol version 6 (IPv6)
   implementations.  They do not override choices made by applications
   or upper-layer protocols, nor do they preclude the development of
   more advanced mechanisms for address selection.  The two algorithms
   share a common context, including an optional mechanism for allowing
   administrators to provide policy that can override the default
   behavior.  In dual-stack implementations, the destination address
   selection algorithm can consider both IPv4 and IPv6 addresses --
   depending on the available source addresses, the algorithm might
   prefer IPv6 addresses over IPv4 addresses, or vice versa.

   Default address selection as defined in this specification applies to
   all IPv6 nodes, including both hosts and routers.  This document
   obsoletes RFC 3484.

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 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/rfc6724.

Thaler, et al.               Standards Track                    [Page 1]
RFC 6724           Default Address Selection for IPv6     September 2012

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
      1.1. Conventions Used in This Document ..........................4
   2. Context in Which the Algorithms Operate .........................4
      2.1. Policy Table ...............................................6
      2.2. Common Prefix Length .......................................7
   3. Address Properties ..............................................7
      3.1. Scope Comparisons ..........................................8
      3.2. IPv4 Addresses and IPv4-Mapped Addresses ...................8
      3.3. Other IPv6 Addresses with Embedded IPv4 Addresses ..........9
      3.4. IPv6 Loopback Address and Other Format Prefixes ............9
      3.5. Mobility Addresses .........................................9
   4. Candidate Source Addresses .....................................10
   5. Source Address Selection .......................................11
   6. Destination Address Selection ..................................14
   7. Interactions with Routing ......................................16
   8. Implementation Considerations ..................................16
   9. Security Considerations ........................................17
   10. Examples ......................................................18
      10.1. Default Source Address Selection .........................18
      10.2. Default Destination Address Selection ....................19
      10.3. Configuring Preference for IPv6 or IPv4 ..................20
           10.3.1. Handling Broken IPv6 ..............................21
      10.4. Configuring Preference for Link-Local Addresses ..........21
      10.5. Configuring a Multi-Homed Site ...........................22
      10.6. Configuring ULA Preference ...............................24