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Internet Engineering Task Force (IETF)                       T. AndersonRequest for Comments: 8215                                Redpill LinproCategory: Standards Track                                    August 2017ISSN: 2070-1721Local-Use IPv4/IPv6 Translation PrefixAbstract   This document reserves the IPv6 prefix 64:ff9b:1::/48 for local use   within domains that enable IPv4/IPv6 translation mechanisms.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 inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8215.Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Anderson                     Standards Track                    [Page 1]

RFC 8215         Local-Use IPv4/IPv6 Translation Prefix      August 2017Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .23.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .24.  Why 64:ff9b:1::/48? . . . . . . . . . . . . . . . . . . . . .34.1.  Prefix Length . . . . . . . . . . . . . . . . . . . . . .34.2.  Prefix Value  . . . . . . . . . . . . . . . . . . . . . .45.  Deployment Considerations . . . . . . . . . . . . . . . . . .46.  Checksum Neutrality . . . . . . . . . . . . . . . . . . . . .57.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .68.  Security Considerations . . . . . . . . . . . . . . . . . . .69.  References  . . . . . . . . . . . . . . . . . . . . . . . . .69.1.  Normative References  . . . . . . . . . . . . . . . . . .69.2.  Informative References  . . . . . . . . . . . . . . . . .7   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .7   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .71.  Introduction   This document reserves 64:ff9b:1::/48 for local use within domains   that enable IPv4/IPv6 translation mechanisms.  This facilitates the   coexistence of multiple IPv4/IPv6 translation mechanisms in the same   network without requiring the use of a Network-Specific Prefix   assigned from the operator's allocated global unicast address space.2.  Terminology   This document uses the following terms:   Network-Specific Prefix (NSP)      A globally unique prefix assigned by a network operator for use      with an IPv4/IPv6 translation mechanism [RFC6052].   Well-Known Prefix (WKP)      The prefix 64:ff9b::/96, which is reserved for use with the      [RFC6052] IPv4/IPv6 address translation algorithms.3.  Problem Statement   Since the WKP 64:ff9b::/96 was reserved by [RFC6052], several new   IPv4/IPv6 translation mechanisms have been defined by the IETF, such   as those defined in [RFC6146] and [RFC7915].  These mechanisms target   various different use cases.  An operator might therefore wish to   make use of several of them simultaneously.   The WKP is reserved specifically for use with the algorithms   specified in [RFC6052].  More recent RFCs describe IPv4/IPv6Anderson                     Standards Track                    [Page 2]

RFC 8215         Local-Use IPv4/IPv6 Translation Prefix      August 2017   translation mechanisms that use different algorithms.  An operator   deploying such mechanisms cannot make use of the WKP in a legitimate   fashion.   Also, because the WKP is a /96, an operator preferring to use the WKP   over an NSP can do so for only one of their IPv4/IPv6 translation   mechanisms.  All others must necessarily use an NSP.Section 3.1 of [RFC6052] imposes certain restrictions on the use of   the WKP, such as forbidding its use in combination with private IPv4   addresses [RFC1918].  These restrictions might conflict with the   operator's desired use of an IPv4/IPv6 translation mechanism.   In summary, there is a need for a local-use prefix that facilitates   the coexistence of multiple IPv4/IPv6 translation mechanisms in a   single network domain, as well as the deployment of translation   mechanisms that do not use the [RFC6052] algorithms or adhere to its   usage restrictions.4.  Why 64:ff9b:1::/48?4.1.  Prefix Length   One of the primary goals of this document is to facilitate multiple   simultaneous deployments of IPv4/IPv6 translation mechanisms in a   single network.  The first criterion is therefore that the prefix   length chosen must be shorter than the prefix length used by any   individual translation mechanism.   The second criterion is that the prefix length chosen is a multiple   of 16.  This ensures the prefix ends on a colon boundary when   representing it in text, easing operator interaction with it.   The [RFC6052] algorithms specifies IPv4/IPv6 translation prefixes as   short as /32.  In order to facilitate multiple instances of   translation mechanisms using /32s, while at the same time aligning on   a 16-bit boundary, it would be necessary to reserve a /16.  Doing so,   however, was considered as too wasteful by the IPv6 Operations   Working Group.   The shortest translation prefix that was reported to the IPv6   Operations Working Group as being deployed in a live network was /64.   The longest 16-bit-aligned prefix length that can accommodate   multiple instances of /64 is /48.  The prefix length of /48 was   therefore chosen, as it satisfies both the criteria above, while at   the same time avoids wasting too much of the IPv6 address space.Anderson                     Standards Track                    [Page 3]

RFC 8215         Local-Use IPv4/IPv6 Translation Prefix      August 20174.2.  Prefix Value   It is desirable to minimise the amount of additional "pollution" in   the unallocated IPv6 address space caused by the reservation made by   this document.  Ensuring the reserved prefix is adjacent to the   64:ff9b::/96 WKP already reserved by [RFC6052] accomplishes this.   Given the previous decision to use a prefix length of /48, this   leaves two options: 64:ff9a:ffff::/48 and 64:ff9b:1::/48.   64:ff9a:ffff::/48 has the benefit that it is completely adjacent to   the [RFC6052] WKP.  That is, 64:ff9a:ffff::/48 and 64:ff9b::/96   combine to form an uninterrupted range of IPv6 addresses starting   with 64:ff9a:ffff:: and ending with 64:ff9b::ffff:ffff.   64:ff9b:1::/48 is, on the other hand, not completely adjacent to   64:ff9b::/96.  The range starting with 64:ff9b::1:0:0 and ending with   64:ff9b:0:ffff:ffff:ffff:ffff:ffff would remain unallocated.   This particular drawback is, however, balanced by the fact that the   smallest possible aggregate prefix that covers both the [RFC6052] WKP   and 64:ff9a:ffff::/48 is much larger than the smallest possible   aggregate prefix that covers both the [RFC6052] WKP and   64:ff9b:1::/48.  These aggregate prefixes are 64:ff9a::/31 and   64:ff9b::/47, respectively.  IPv6 address space is allocated using   prefixes rather than address ranges, so it could be argued that   64:ff9b:1::/48 is the option that would cause special-use prefixes   reserved for IPv4/IPv6 translation to "pollute" the minimum possible   amount of unallocated IPv6 address space.   Finally, 64:ff9b:1::/48 also has the advantage that its textual   representation is shorter than 64:ff9a:ffff::/48.  While this might   seem insignificant, the preference human network operators have for   addresses that are simple to type should not be underestimated.   After weighing the above pros and cons, 64:ff9b:1::/48 was chosen.5.  Deployment Considerations   64:ff9b:1::/48 is intended as a technology-agnostic and generic   reservation.  A network operator may freely use it in combination   with any kind of IPv4/IPv6 translation mechanism deployed within   their network.   By default, IPv6 nodes and applications must not treat IPv6 addresses   within 64:ff9b:1::/48 differently from other globally scoped IPv6   addresses.  In particular, they must not make any assumptions   regarding the syntax or properties of those addresses (e.g., theAnderson                     Standards Track                    [Page 4]

RFC 8215         Local-Use IPv4/IPv6 Translation Prefix      August 2017   existence and location of embedded IPv4 addresses) or the type of   associated translation mechanism (e.g., whether it is stateful or   stateless).   64:ff9b:1::/48 or any more-specific prefix may only be used in inter-   domain routing if done in accordance with the rules described inSection 3.2 of [RFC6052].   Note that 64:ff9b:1::/48 (or any more-specific prefix) is distinct   from the WKP 64:ff9b::/96.  Therefore, the restrictions on the use of   the WKP described inSection 3.1 of [RFC6052] do not apply to the use   of 64:ff9b:1::/48.   Operators tempted to use the covering aggregate prefix 64:ff9b::/47   to refer to all special-use prefixes currently reserved for IPv4/IPv6   translation should be warned that this aggregate includes a range of   unallocated addresses (seeSection 4.2) that the IETF could   potentially reserve in the future for entirely different purposes.6.  Checksum Neutrality   Use of 64:ff9b:1::/48 does not in itself guarantee checksum   neutrality, as many of the IPv4/IPv6 translation algorithms it can be   used with are fundamentally incompatible with checksum-neutral   address translations.Section 4.1 of [RFC6052] contains further discussion about IPv4/IPv6   translation and checksum neutrality.   The Stateless IP/ICMP Translation algorithm [RFC7915] is one well-   known algorithm that can operate in a checksum-neutral manner, when   using the [RFC6052] algorithms for all of its address translations.   However, in order to attain checksum neutrality, it is imperative   that the translation prefix be chosen carefully.  Specifically, in   order for a 96-bit [RFC6052] prefix to be checksum neutral, all the   six 16-bit words in the prefix must add up to a multiple of 0xffff.   The following non-exhaustive list contains examples of translation   prefixes that are checksum neutral when used with the [RFC7915] and   [RFC6052] algorithms:   o  64:ff9b:1:fffe::/96   o  64:ff9b:1:fffd:1::/96   o  64:ff9b:1:fffc:2::/96   o  64:ff9b:1:abcd:0:5431::/96Anderson                     Standards Track                    [Page 5]

RFC 8215         Local-Use IPv4/IPv6 Translation Prefix      August 20177.  IANA Considerations   The IANA has added the following entry to the "IANA IPv6 Special-   Purpose Address Registry":              +----------------------+---------------------+              | Attribute            | Value               |              +----------------------+---------------------+              | Address Block        | 64:ff9b:1::/48      |              | Name                 | IPv4-IPv6 Translat. |              | RFC                  |RFC 8215            |              | Allocation Date      | 2017-06             |              | Termination Date     | N/A                 |              | Source               | True                |              | Destination          | True                |              | Forwardable          | True                |              | Globally Reachable   | False               |              | Reserved-by-Protocol | False               |              +----------------------+---------------------+   The IANA has also added the following footnote to the 0000::/8 entry   of the "Internet Protocol Version 6 Address Space" registry:      64:ff9b:1::/48 reserved for Local-Use IPv4/IPv6 Translation      [RFC8215].8.  Security Considerations   The reservation of 64:ff9b:1::/48 is not known to cause any new   security considerations beyond those documented inSection 5 of   [RFC6052].9.  References9.1.  Normative References   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.              Li, "IPv6 Addressing of IPv4/IPv6 Translators",RFC 6052,              DOI 10.17487/RFC6052, October 2010,              <https://www.rfc-editor.org/info/rfc6052>.Anderson                     Standards Track                    [Page 6]

RFC 8215         Local-Use IPv4/IPv6 Translation Prefix      August 20179.2.  Informative References   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,              and E. Lear, "Address Allocation for Private Internets",BCP 5,RFC 1918, DOI 10.17487/RFC1918, February 1996,              <https://www.rfc-editor.org/info/rfc1918>.   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful              NAT64: Network Address and Protocol Translation from IPv6              Clients to IPv4 Servers",RFC 6146, DOI 10.17487/RFC6146,              April 2011, <https://www.rfc-editor.org/info/rfc6146>.   [RFC7915]  Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,              "IP/ICMP Translation Algorithm",RFC 7915,              DOI 10.17487/RFC7915, June 2016,              <https://www.rfc-editor.org/info/rfc7915>.Acknowledgements   The author would like to thank Fred Baker, Mohamed Boucadair,   Brian E. Carpenter, Pier Carlo Chiodi, Joe Clarke, David Farmer,   Suresh Krishnan, Warren Kumari, Holger Metschulat, Federico   Santandrea, and David Schinazi for contributing to the creation of   this document.Author's Address   Tore Anderson   Redpill Linpro   Vitaminveien 1A   0485 Oslo   Norway   Phone: +47 959 31 212   Email: tore@redpill-linpro.com   URI:http://www.redpill-linpro.comAnderson                     Standards Track                    [Page 7]