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.
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Byrne Standards Track [Page 1]
RFC 7335 IPv4 Service Continuity Prefix August 2014
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.
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].
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 2014
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.