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Internet Engineering Task Force (IETF)                          C. ByrneRequest for Comments: 7335                                   T-Mobile USUpdates:6333                                                August 2014Category: Standards TrackISSN: 2070-1721IPv4 Service Continuity PrefixAbstract   Dual-Stack Lite (DS-Lite), defined inRFC 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 inSection 2 of RFC 5741.   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/rfc7335.Copyright Notice   Copyright (c) 2014 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.Byrne                        Standards Track                    [Page 1]

RFC 7335             IPv4 Service Continuity Prefix          August 2014Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .23.  The Case of 464XLAT  . . . . . . . . . . . . . . . . . . . . .24.  Choosing 192.0.0.0/29  . . . . . . . . . . . . . . . . . . . .35.  Security Considerations  . . . . . . . . . . . . . . . . . . .36.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .37.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .48.  Normative References . . . . . . . . . . . . . . . . . . . . .41.  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.Byrne                        Standards Track                    [Page 2]

RFC 7335             IPv4 Service Continuity Prefix          August 20144.  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]Byrne                        Standards Track                    [Page 3]

RFC 7335             IPv4 Service Continuity Prefix          August 2014      +----------------------+-----------------------------------+      | 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",RFC6877, April 2013.Author's Address   Cameron Byrne   Bellevue, WA   USA   EMail: Cameron.Byrne@T-Mobile.comByrne                        Standards Track                    [Page 4]