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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
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.






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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.










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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]











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+----------------------+-----------------------------------+
| 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










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