IPv4 Service Continuity Prefix
One small reserved IPv4 block, now shared by every IPv6 transition tool that needs a non-routed IPv4 address.
Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335, DOI 10.17487/RFC7335, August 2014, <https://www.rfc-editor.org/info/rfc7335>.
@misc{rfc7335,
series = {Request for Comments},
number = 7335,
howpublished = {RFC 7335},
publisher = {RFC Editor},
doi = {10.17487/RFC7335},
url = {https://www.rfc-editor.org/info/rfc7335},
author = {C. Byrne},
title = {{IPv4 Service Continuity Prefix}},
pagetotal = 4,
year = 2014,
month = aug,
} RFC text
Contents
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.
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
AI ELI5
On this page
§1Generalizing a DS-Lite Reservation
RFC 6333 (DS-Lite) told IANA to reserve 192.0.0.0/29 for the Basic Bridging BroadBand (B4) element. RFC 7335 widens that reservation to cover any case where a non-routed IPv4 interface must be numbered as part of an IPv6 transition solution.
The block is now called the IPv4 Service Continuity Prefix. It may be used in any system that needs IPv4 addresses for backward compatibility in an IPv6-only network but does not emit IPv4 packets on the wire. The change does not affect its use in DS-Lite.
A club saved a few special seat numbers for one kind of guest. Now other kinds of guests can use those seat numbers too.
§2The Case of 464XLAT
464XLAT (RFC 6877) provides IPv4 communication over an IPv6-only access network. In one of its methods the customer-side translator (CLAT) is embedded in a host such as a smartphone or a CPE (Customer Premises Equipment).
In that setup the host must have an IPv4 address configured so the host network stack and applications can bind IPv4 sockets. The address has to be locally unique to avoid conflicts with any other network that may talk to the CLAT.
A phone that only speaks the new language still needs an old-style address to give to its apps, even if that address never leaves the phone.
§3Choosing 192.0.0.0/29
In RFC 6333 this subnet exists only 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, and other similar solutions may too, so the RFC judges it most prudent to generalize the one prefix rather than reserve a new one for every possible solution.
There is one rule: 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.
Everyone shares the same set of seat numbers, so one person must not use two helpers that both grab the same seats at once.
§4IANA and Security Notes
IANA changed the IPv4 Special-Purpose Address Registry entry for 192.0.0.0/29 from "DS-Lite" (RFC 6333) to "IPv4 Service Continuity Prefix" (RFC 7335). The registry attributes include Source True, Destination True, Forwardable True, Global False and Reserved-by-Protocol False.
The RFC adds no security considerations beyond those in RFC 6333 and RFC 6877.
The big list of special addresses now has a new label on this entry, and nothing new to worry about.