Analysis of the 64-bit Boundary in IPv6 Addressing
RFC 7421

Document Type RFC - Informational (January 2015; No errata)
Last updated 2015-10-14
Replaces draft-carpenter-6man-why64
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Internet Engineering Task Force (IETF)                 B. Carpenter, Ed.
Request for Comments: 7421                             Univ. of Auckland
Category: Informational                                         T. Chown
ISSN: 2070-1721                                     Univ. of Southampton
                                                                 F. Gont
                                                  SI6 Networks / UTN-FRH
                                                                S. Jiang
                                            Huawei Technologies Co., Ltd
                                                             A. Petrescu
                                                               CEA, LIST
                                                          A. Yourtchenko
                                                                   Cisco
                                                            January 2015

           Analysis of the 64-bit Boundary in IPv6 Addressing

Abstract

   The IPv6 unicast addressing format includes a separation between the
   prefix used to route packets to a subnet and the interface identifier
   used to specify a given interface connected to that subnet.
   Currently, the interface identifier is defined as 64 bits long for
   almost every case, leaving 64 bits for the subnet prefix.  This
   document describes the advantages of this fixed boundary and analyzes
   the issues that would be involved in treating it as a variable
   boundary.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc7421.

Carpenter, et al.             Informational                     [Page 1]
RFC 7421                         Why 64                     January 2015

Copyright Notice

   Copyright (c) 2015 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
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   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
   2.  Advantages of a Fixed Identifier Length . . . . . . . . . . .   4
   3.  Arguments for Shorter Identifier Lengths  . . . . . . . . . .   5
     3.1.  Insufficient Address Space Delegated  . . . . . . . . . .   5
     3.2.  Hierarchical Addressing . . . . . . . . . . . . . . . . .   6
     3.3.  Audit Requirement . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Concerns over ND Cache Exhaustion . . . . . . . . . . . .   7
   4.  Effects of Varying the Interface Identifier Length  . . . . .   8
     4.1.  Interaction with IPv6 Specifications  . . . . . . . . . .   8
     4.2.  Possible Failure Modes  . . . . . . . . . . . . . . . . .  10
     4.3.  Experimental Observations . . . . . . . . . . . . . . . .  12
       4.3.1.  Survey of the processing of Neighbor Discovery
               Options with Prefixes Other than /64  . . . . . . . .  12
       4.3.2.  Other Observations  . . . . . . . . . . . . . . . . .  14
     4.4.  Implementation and Deployment Issues  . . . . . . . . . .  14
     4.5.  Privacy Issues  . . . . . . . . . . . . . . . . . . . . .  16
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Acknowledgements .  . . . . . . . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

Carpenter, et al.             Informational                     [Page 2]
RFC 7421                         Why 64                     January 2015
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