Reserved IPv6 Interface Identifiers
RFC 5453

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Network Working Group                                        S. Krishnan
Request for Comments: 5453                                      Ericsson
Category: Standards Track                                  February 2009

                  Reserved IPv6 Interface Identifiers

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) 2009 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.

Abstract

   Interface identifiers in IPv6 unicast addresses are used to identify
   interfaces on a link.  They are required to be unique within a
   subnet.  Several RFCs have specified interface identifiers or
   identifier ranges that have a special meaning attached to them.  An
   IPv6 node autoconfiguring an interface identifier in these ranges
   will encounter unexpected consequences.  Since there is no
   centralized repository for such reserved identifiers, this document
   aims to create one.

Krishnan                    Standards Track                     [Page 1]
RFC 5453          Reserved IPv6 Interface Identifiers      February 2009

Table of Contents

   1. Introduction ....................................................2
      1.1. Applicability ..............................................2
      1.2. Requirements Notation ......................................3
   2. Issues with Reusing Reserved Interface Identifiers ..............3
      2.1. Possible Solutions .........................................3
   3. IANA Considerations .............................................3
   4. Acknowledgements ................................................4
   5. Security Considerations .........................................4
   6. References ......................................................5
      6.1. Normative References .......................................5
      6.2. Informative References .....................................5
   Appendix A. List of Potentially Affected RFCs ......................6

1.  Introduction

   An IPv6 unicast address is composed of two parts: a subnet prefix and
   an interface identifier (IID) that identifies a unique interface
   within the subnet prefix.  The structure of an IPv6 unicast address
   is depicted in "IPv6 Addressing Architecture" [RFC4291] and is
   replicated here for clarity.

   |          n bits               |           128-n bits            |
   +-------------------------------+---------------------------------+
   |       subnet prefix           |           interface ID          |
   +-------------------------------+---------------------------------+

                   Figure 1: IPv6 Unicast Address Format

   For all unicast addresses, except those that start with the binary
   value 000, Interface IDs are required to be 64 bits long and to be
   constructed in Modified EUI-64 format [RFC4291].  Examples of
   mechanisms that generate interface identifiers without a unique token
   include Cryptographically Generated Addresses [RFC3972], Privacy
   Addresses [RFC4941], Hash-Based Addresses [HBA], etc.  Non-unique
   interface identifiers can also be allocated using managed address
   assignment mechanisms like DHCPv6 (Dynamic Host Configuration
   Protocol for IPv6) [RFC3315].

1.1.  Applicability

   This document applies only to interface identifiers that are formed
   in the modified EUI-64 format as defined in Appendix A of [RFC4291].
   All other types of interface identifiers are out of its scope.

Krishnan                    Standards Track                     [Page 2]
RFC 5453          Reserved IPv6 Interface Identifiers      February 2009

1.2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Issues with Reusing Reserved Interface Identifiers

   Let us assume a node comes up with an interface identifier that has
   been reserved for use in some other capacity, e.g., an IPv6 node that
   uses temporary IPv6 addresses [RFC4941] comes up with an IID of
   fdff:ffff:ffff:ffff.  This node will receive requests from all nodes
   that are requesting a service from a Mobile IPv6 home agent since the
   above-mentioned interface identifier has been reserved in [RFC2526]