Default Address Selection for Internet Protocol version 6 (IPv6)
RFC 3484

Document Type RFC - Proposed Standard (March 2003; No errata)
Obsoleted by RFC 6724
Last updated 2015-10-14
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IESG IESG state RFC 3484 (Proposed Standard)
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Responsible AD Thomas Narten
IESG note 2003-03-04: RFC 3484 appears
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Network Working Group                                          R. Draves
Request for Comments: 3484                            Microsoft Research
Category: Standards Track                                  February 2003

   Default Address Selection for Internet Protocol version 6 (IPv6)

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 (2003).  All Rights Reserved.

Abstract

   This document describes two algorithms, for source address selection
   and 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.

   All IPv6 nodes, including both hosts and routers, must implement
   default address selection as defined in this specification.

Draves                      Standards Track                     [Page 1]
RFC 3484           Default Address Selection for IPv6      February 2003

Table of Contents

   1.    Introduction................................................2
         1.1.  Conventions Used in This Document.....................4
   2.    Context in Which the Algorithms Operate.....................4
         2.1.  Policy Table..........................................5
         2.2.  Common Prefix Length..................................6
   3.    Address Properties..........................................6
         3.1.  Scope Comparisons.....................................7
         3.2.  IPv4 Addresses and IPv4-Mapped Addresses..............7
         3.3.  Other IPv6 Addresses with Embedded IPv4 Addresses.....8
         3.4.  IPv6 Loopback Address and Other Format Prefixes.......8
         3.5.  Mobility Addresses....................................8
   4.    Candidate Source Addresses..................................8
   5.    Source Address Selection...................................10
   6.    Destination Address Selection..............................12
   7.    Interactions with Routing..................................14
   8.    Implementation Considerations..............................15
   9.    Security Considerations....................................15
   10.   Examples...................................................16
         10.1. Default Source Address Selection.....................16
         10.2. Default Destination Address Selection................17
         10.3. Configuring Preference for IPv6 or IPv4..............18
         10.4. Configuring Preference for Scoped Addresses..........19
         10.5. Configuring a Multi-Homed Site.......................19
   Normative References.............................................21
   Informative References...........................................22
   Acknowledgments..................................................23
   Author's Address.................................................23
   Full Copyright Statement.........................................24

1. Introduction

   The IPv6 addressing architecture [1] allows multiple unicast
   addresses to be assigned to interfaces.  These addresses may have
   different reachability scopes (link-local, site-local, or global).
   These addresses may also be "preferred" or "deprecated" [2].  Privacy
   considerations have introduced the concepts of "public addresses" and
   "temporary addresses" [3].  The mobility architecture introduces
   "home addresses" and "care-of addresses" [8].  In addition, multi-
   homing situations will result in more addresses per node.  For
   example, a node may have multiple interfaces, some of them tunnels or
   virtual interfaces, or a site may have multiple ISP attachments with
   a global prefix per ISP.

   The end result is that IPv6 implementations will very often be faced
   with multiple possible source and destination addresses when
   initiating communication.  It is desirable to have default
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