Internet Engineering Task Force (IETF)                          C. Byrne
Request for Comments: 7335                                   T-Mobile US
Updates: 6333                                                August 2014
Category: Standards Track
ISSN: 2070-1721


                     IPv4 Service Continuity Prefix

Abstract

   Dual-Stack Lite (DS-Lite), defined in RFC 6333, directs IANA to
   reserve 192.0.0.0/29 for the Basic Bridging BroadBand (B4) element.
   Per this memo, IANA has generalized that reservation to include other
   cases where a non-routed IPv4 interface must be numbered as part of
   an IPv6 transition solution.

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 in 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/rfc7335.

Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  2
   3.  The Case of 464XLAT  . . . . . . . . . . . . . . . . . . . . .  2
   4.  Choosing 192.0.0.0/29  . . . . . . . . . . . . . . . . . . . .  3
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  3
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  3
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  4
   8.  Normative References . . . . . . . . . . . . . . . . . . . . .  4

1.  Introduction

   DS-Lite [RFC6333] directs IANA to reserve 192.0.0.0/29 for the Basic
   Bridging BroadBand (B4) element.  This memo generalizes that IANA
   reservation to include other cases where a non-routed IPv4 interface
   must be numbered in an IPv6 transition solution.  IANA has listed the
   address block 192.0.0.0/29 reserved for IPv4 Service Continuity
   Prefix.  The result is that 192.0.0.0/29 may be used in any system
   that requires IPv4 addresses for backward compatibility with IPv4
   communications in an IPv6-only network but does not emit IPv4 packets
   "on the wire".

   This generalization does not impact the use of the IPv4 Service
   Continuity Prefix in a DS-Lite context.

2.  Conventions

   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.  The Case of 464XLAT

   464XLAT [RFC6877] describes an architecture for providing IPv4
   communication over an IPv6-only access network.  One of the methods
   described in [RFC6877] is for the customer-side translator (CLAT) to
   be embedded in the host, such as a smartphone or a CPE (Customer
   Premises Equipment).  In such scenarios, the host must have an IPv4
   address configured to present to the host network stack and for
   applications to bind IPv4 sockets.

4.  Choosing 192.0.0.0/29

   To avoid conflicts with any other network that may communicate with
   the CLAT or other IPv6 transition solution, a locally unique IPv4
   address must be assigned.

   IANA has defined a well-known range, 192.0.0.0/29, in [RFC6333],
   which is dedicated for DS-Lite.  As defined in [RFC6333], this subnet
   is only present between the B4 and the Address Family Transition
   Router (AFTR) and never emits packets from this prefix "on the wire".
   464XLAT has the same need for a non-routed IPv4 prefix, and this same
   need may be common for other similar solutions.  It is most prudent
   and effective to generalize 192.0.0.0/29 for the use of supporting
   IPv4 interfaces in IPv6 transition technologies rather than reserving
   a prefix for every possible solution.

   With this memo, 192.0.0.0/29 is now generalized across multiple IPv4
   continuity solutions such as 464XLAT and DS-Lite.  A host MUST NOT
   enable two active IPv4 continuity solutions simultaneously in a way
   that would cause a node to have overlapping 192.0.0.0/29 address
   space.

5.  Security Considerations

   There are no new security considerations beyond what is described
   [RFC6333] and [RFC6877].

6.  IANA Considerations

   IANA has updated the IPv4 Special-Purpose Address Registry available
   at (http://www.iana.org/assignments/iana-ipv4-special-registry/) as
   follows:

   OLD:

   192.0.0.0/29    DS-Lite         [RFC6333]

   NEW:

   192.0.0.0/29    IPv4 Service Continuity Prefix  [RFC7335]

      +----------------------+-----------------------------------+
      | Attribute            | Value                             |
      +----------------------+-----------------------------------+
      | Address Block        | 192.0.0.0/29                      |
      | Name                 | IPv4 Service Continuity Prefix    |
      | RFC                  | RFC 7335                          |
      | Allocation Date      | June 2011                         |
      | Termination Date     | N/A                               |
      | Source               | True                              |
      | Destination          | True                              |
      | Forwardable          | True                              |
      | Global               | False                             |
      | Reserved-by-Protocol | False                             |
      +----------------------+-----------------------------------+

7.  Acknowledgements

   This document has been substantially improved by specific feedback
   from Dave Thaler, Fred Baker, Wes George, Lorenzo Colitti, and
   Mohamed Boucadair.

8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation", RFC
              6877, April 2013.

Author's Address

   Cameron Byrne
   Bellevue, WA
   USA

   EMail: Cameron.Byrne@T-Mobile.com