



Internet Engineering Task Force (IETF)                      B. Carpenter
BCP: 242                                               Univ. of Auckland
Request for Comments: 9812                                   S. Krishnan
Updates: 7249                                                      Cisco
Category: Best Current Practice                                D. Farmer
ISSN: 2070-1721                                       Univ. of Minnesota
                                                            October 2025


            Clarification of IPv6 Address Allocation Policy

Abstract

   This document specifies the approval process for changes to the "IPv6
   Address Space" registry.  It also updates RFC 7249.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   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
   BCPs is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9812.

Copyright Notice

   Copyright (c) 2025 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
   (https://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
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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Approval Level of IPv6 Address Allocations
   3.  IANA Considerations
   4.  Security Considerations
   5.  References
     5.1.  Normative References
     5.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Internet Protocol Version 6 (IPv6) and its address space are defined
   by [STD86] and [RFC4291].  The management of the IPv6 address space
   was delegated to IANA by [RFC1881], some years before the
   relationship between the IETF and IANA was formalized [RFC2860] and
   registry details were clarified [RFC7020] [RFC7249].

   Occasionally, IPv6 address space allocations are performed outside
   the scope of routine allocations to Regional Internet Registries
   (RIRs).  For example, a substantial allocation was requested by an
   IETF document approved by the IESG [RFC9602], which moved the range
   5f00::/16 from the "IPv6 Address Space" registry [IANA1] to the "IPv6
   Special-Purpose Address Space" registry [IANA3].

   At the time of writing, the allocation policy in the "IPv6 Address
   Space" registry [IANA1] was shown as "IESG approval", whereas a more
   stringent policy is appropriate for major allocations.  The present
   document therefore strengthens the approval level needed for non-
   routine address allocations, which requires an update to [RFC7249].

   This document also clarifies the status of [RFC1881].  This
   clarification is necessary because [RFC1881], a joint publication of
   the IAB and IESG following an IETF Last Call, was incorrectly listed
   in the RFC index at the time of writing as "Legacy", whereas it is
   part of the IETF Stream [RFC8729].

2.  Approval Level of IPv6 Address Allocations

   Portions of the IPv6 address space are shown in the registry as
   "Reserved by IETF" [IANA1].  This is the address space held in
   reserve for future use if ever the 125-bit unicast space (2000::/3)
   is found inadequate or inappropriate.

   [RFC1881] did not specify an allocation policy for this space.  At
   some point, IANA listed "IESG approval".  As defined in [BCP26], this
   is a rather weak requirement ("Although there is no requirement that
   the request be documented in an RFC, the IESG has the discretion to
   request documents...") and is "a fall-back mechanism in the case
   where one of the other allowable approval mechanisms cannot be
   employed...".

   For something as important as the majority of the spare IPv6 address
   space, this process is clearly insufficient.  The present document
   replaces the "IESG approval" process by the "IETF Review" process as
   defined by [BCP26].  The stricter "Standards Action" policy is not
   considered necessary, because there may be cases where opening up a
   new range of address space does not in fact require a new protocol
   standard.

   It may be noted that the allocation for [RFC9602], which was
   processed as a working group document, did indeed follow the more
   stringent "IETF Review" process proposed by this document.  Indeed,
   the other two related registries [IANA2] [IANA3] cite the "IETF
   Review" policy, consistent with [RFC7249].

   This document therefore extends the first paragraph of Section 2.3 of
   [RFC7249] as follows:

   OLD:

   |  The vast bulk of the IPv6 address space (approximately 7/8ths of
   |  the whole address space) is reserved by the IETF [RFC4291], with
   |  the expectation that further assignment of globally unique unicast
   |  address space will be made from this reserved space in accordance
   |  with future needs.

   NEW:

   |  The vast bulk of the IPv6 address space (approximately 7/8ths of
   |  the whole address space) is reserved by the IETF [RFC4291], with
   |  the expectation that further assignment of globally unique unicast
   |  address space will be made from this reserved space in accordance
   |  with future needs, through "IETF Review" as defined in [BCP26].

3.  IANA Considerations

   IANA has updated the registration procedure of the "IPv6 Address
   Space" registry [IANA1] to "IETF Review".

4.  Security Considerations

   The security considerations of [RFC7249] apply.  While having no
   direct security impact, carefully reviewed address allocation
   mechanisms are necessary to ensure operational address
   accountability.

5.  References

5.1.  Normative References

   [BCP26]    Best Current Practice 26,
              <https://www.rfc-editor.org/info/bcp26>.
              At the time of writing, this BCP comprises the following:

              Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [STD86]    Internet Standard 86,
              <https://www.rfc-editor.org/info/std86>.
              At the time of writing, this STD comprises the following:

              Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

5.2.  Informative References

   [IANA1]    IANA, "IPv6 Address Space",
              <https://www.iana.org/assignments/ipv6-address-space>.

   [IANA2]    IANA, "IPv6 Global Unicast Address Space",
              <https://www.iana.org/assignments/ipv6-unicast-address-
              assignments>.

   [IANA3]    IANA, "IPv6 Special-Purpose Address Space",
              <https://www.iana.org/assignments/iana-ipv6-special-
              registry>.

   [RFC1881]  IAB and IESG, "IPv6 Address Allocation Management",
              RFC 1881, DOI 10.17487/RFC1881, December 1995,
              <https://www.rfc-editor.org/info/rfc1881>.

   [RFC2860]  Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
              Understanding Concerning the Technical Work of the
              Internet Assigned Numbers Authority", RFC 2860,
              DOI 10.17487/RFC2860, June 2000,
              <https://www.rfc-editor.org/info/rfc2860>.

   [RFC7020]  Housley, R., Curran, J., Huston, G., and D. Conrad, "The
              Internet Numbers Registry System", RFC 7020,
              DOI 10.17487/RFC7020, August 2013,
              <https://www.rfc-editor.org/info/rfc7020>.

   [RFC7249]  Housley, R., "Internet Numbers Registries", RFC 7249,
              DOI 10.17487/RFC7249, May 2014,
              <https://www.rfc-editor.org/info/rfc7249>.

   [RFC8729]  Housley, R., Ed. and L. Daigle, Ed., "The RFC Series and
              RFC Editor", RFC 8729, DOI 10.17487/RFC8729, February
              2020, <https://www.rfc-editor.org/info/rfc8729>.

   [RFC9602]  Krishnan, S., "Segment Routing over IPv6 (SRv6) Segment
              Identifiers in the IPv6 Addressing Architecture",
              RFC 9602, DOI 10.17487/RFC9602, October 2024,
              <https://www.rfc-editor.org/info/rfc9602>.

Acknowledgements

   Useful comments were received from Dale Carder, Bob Hinden, Scott
   Kelly, Philipp Tiesel, and others.

Authors' Addresses

   Brian E. Carpenter
   The University of Auckland
   School of Computer Science
   PB 92019
   Auckland 1142
   New Zealand
   Email: brian.e.carpenter@gmail.com


   Suresh Krishnan
   Cisco Systems, Inc.
   Email: suresh.krishnan@gmail.com


   David E. Farmer III
   University of Minnesota
   Office of Information Technology
   Minneapolis, MN 55455
   United States of America
   Email: farmer@umn.edu
