Local-use IPv4/IPv6 Translation Prefix
draft-ietf-v6ops-v4v6-xlat-prefix-00

IPv6 Operations                                              T. Anderson
Internet-Draft                                            Redpill Linpro
Updates: 6890 (if approved)                                March 9, 2017
Intended status: Standards Track
Expires: September 10, 2017

                 Local-use IPv4/IPv6 Translation Prefix
                  draft-ietf-v6ops-v4v6-xlat-prefix-00

Abstract

   This document reserves the IPv6 prefix 64:ff9b:1::/48 for local use
   within domains that enable IPv4/IPv6 translation mechanisms.  This
   document updates RFC6890.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Why 64:ff9b:1::/48? . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Prefix Length . . . . . . . . . . . . . . . . . . . . . .   3
     4.2.  Prefix Value  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Deployment Considerations . . . . . . . . . . . . . . . . . .   4
   6.  Checksum Neutrality . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document reserves 64:ff9b:1::/48 for local use within domains
   that enable IPv4/IPv6 translation mechanisms.  This facilitates the
   co-existence 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 makes use of 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 algorithm.

   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].

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.
   These mechanisms target various different use cases.  An operator
   might therefore wish to make use of several of them simultaneously.

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   The WKP is reserved specifically for use with the algorithm specified
   in [RFC6052].  More recent IETF documents describe IPv4/IPv6
   translation mechanisms that use different algorithms.  An operator
   deploying such mechanisms can not make use of the WKP in a legitimate
   fashion.

   Also, because the WKP is a /96, an operator preferring to use a WKP
   over an NSP can only do so for only one of his 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 co-existence 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] algorithm 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 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] algorithm 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
   was however considered as too wasteful by the IPv6 Operations working
   group.

   The shortest translation prefix that was reported to the IPv6
   Operations working group to be 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.

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4.2.  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:ffff::/48 and 64:ff9b:1::/48.

   64:ff9a:ffff:ffff::/48 has the benefit that it is completely adjacent
   to the [RFC6052] WKP.  That is, 64:ff9a:ffff:ffff::/48 and
   64:ff9b::/96 combines to form a uninterrupted range of IPv6 addresses
   starting with 64:ff9a:ffff: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:ffff::/48 is much larger than the smallest possible
   aggregate prefix that covers both the [RFC6052] WKP and
   64:ff9b:1::/96.  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::/96 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 considerably shorter than 64:ff9a:ffff: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 his
   network.

   By default, IPv6 nodes and applications must not treat IPv6 addresses
   within 64:ff9b:1::/48 different from other globally scoped IPv6
   addresses.  In particular, they must not make any assumptions

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   regarding the syntax or properties of those addresses (e.g., the
   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 other more-specific prefix SHOULD NOT be
   advertised in inter-domain routing, except by explicit agreement
   between all involved parties.  Such prefixes MUST NOT be advertised
   to the default-free zone.

   When 64:ff9b:1::/48 or a more-specific prefix is used with the
   [RFC6052] algorithm, it is considered to be a Network-Specific
   Prefix.

   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 (Section 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.

   The Stateless IP/ICMP Translation algorithm [RFC7915] is one well-
   known algorithm that can operate in a checksum-neutral manner, when
   using the [RFC6052] algorithm for all of its address translations.
   However, in order to attain checksum neutrality is imperative that
   the translation prefix is 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::/96

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   Section 4.1 of [RFC6052] contains further discussion about IPv4/IPv6
   translation and checksum neutrality.

7.  IANA Considerations

   The IANA is requested to add the following entry to the IPv6 Special-
   Purpose Address Registry:

              +----------------------+---------------------+
              | Attribute            | Value               |
              +----------------------+---------------------+
              | Address Block        | 64:ff9b:1::/48      |
              | Name                 | IPv4-IPv6 Translat. |
              | RFC                  | (TBD)               |
              | Allocation Date      | (TBD)               |
              | Termination Date     | N/A                 |
              | Source               | True                |
              | Destination          | True                |
              | Forwardable          | True                |
              | Global               | False               |
              | Reserved-by-Protocol | False               |
              +----------------------+---------------------+

   The IANA is furthermore requested to add 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 [TBD]

8.  Security Considerations

   The reservation of 64:ff9b:1::/48 is not known to cause any new
   security considerations beyond those documented in Section 5 of
   [RFC6052].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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,
              <http://www.rfc-editor.org/info/rfc6052>.

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9.2.  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,
              <http://www.rfc-editor.org/info/rfc1918>.

   [RFC7915]  Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
              "IP/ICMP Translation Algorithm", RFC 7915,
              DOI 10.17487/RFC7915, June 2016,
              <http://www.rfc-editor.org/info/rfc7915>.

Appendix A.  Acknowledgements

   The author would like to thank Fred Baker, Mohamed Boucadair, Brian E
   Carpenter, Pier Carlo Chiodi, David Farmer, Holger Metschulat 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.com

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