Network Working Group                                           J. Abley
Internet-Draft                                                       ISC
Expires: January 11, 2006                                  July 10, 2005


                     Shim6 Applicability Statement
                   draft-ietf-shim6-applicability-00

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document discusses the applicability of the Shim6 IPv6 protocol
   element and associated support protocols to provide site multihoming
   capabilities in IPv6.

Note on Shim6 Maturity

   Shim6 is a work in progress, and does not currently meet the maturity
   requirements for advancement to Proposed Standard.




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   A summary of the maturity of the various technical specifications
   that accompany this document can be found in Section 6.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.   Architectural Overview . . . . . . . . . . . . . . . . . . . . 3
   3.   Applicability  . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.   Implementations  . . . . . . . . . . . . . . . . . . . . . . . 3
   5.   Operational Experience . . . . . . . . . . . . . . . . . . . . 4
   6.   Maturity Assessment  . . . . . . . . . . . . . . . . . . . . . 4
   7.   Security Considerations  . . . . . . . . . . . . . . . . . . . 4
   8.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 4
   9.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
   10.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     10.1   Normative References . . . . . . . . . . . . . . . . . . . 4
     10.2   Informative References . . . . . . . . . . . . . . . . . . 4
        Author's Address . . . . . . . . . . . . . . . . . . . . . . . 5
   A.   Change History . . . . . . . . . . . . . . . . . . . . . . . . 5
        Intellectual Property and Copyright Statements . . . . . . . . 6































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.  Introduction

   Site multi-homing is an arrangement by which a site may use multiple
   paths to the rest of the Internet, to provide better reliability for
   traffic passing in and out of the site than would be possible with a
   single path.  Some of the motivations for operators to multi-home
   their network are described in [RFC3582].

   In IPv4, site multi-homing is achieved by introducing the additional
   state required to allow session resilience over re-homing events to
   the global Internet routing system (sometimes referred to as the
   Default-Free Zone, or DFZ) [I-D.ietf-multi6-v4-multihoming].  There
   is concern that this approach will not scale [RFC3221].

   In IPv6, site multi-homing in the style of IPv4 is not generally
   available to end sites due to a strict route aggregation in the DFZ,
   coupled with Regional Internet Registry (RIR) allocation policies
   which prohibit the direct assignment of provider-independent (PI)
   addresses to most end users.  Site multi-homing for sites without PI
   addresses is achieved by assigning multiple addresses to each host,
   one from each provider.  This multi-homing approach provides no
   transport-layer stability across re-homing events.

   Shim6 introduces transport-layer mobility across re-homing events
   using a layer-3 shim approach.  State information relating to the
   multi-homing of two endpoints exchanging unicast traffic is retained
   on the endpoints themselves, rather than in the network.
   Communications between shim6-capable hosts and shim6-incapable hosts
   proceed as normal, but without the benefit of transport-layer
   stability.  The Shim6 approach is thought to have better scaling
   properties than the IPv4 approach, at the expense of somewhat reduced
   operational capability.

.  Architectural Overview

   A general architectural overview of Shim6 will be included here.  In
   the absense of useful text in this section, readers may wish to refer
   to [I-D.ietf-shim6-arch].

.  Applicability

   A list of shim6 technical specifications will go here, each with a
   requirements level, per [RFC2026].

.  Implementations

   There is no known implementation of Shim6.




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.  Operational Experience

   There is no known operational experience of Shim6.

.  Maturity Assessment

   Shim6 is not sufficiently mature at the time of writing to be
   advanced to Proposed Standard [RFC2026].  The following is a list of
   possible work remaining before such advancement might be sought:

   o  The Shim6 technical specifications enumerated in this document are
      not yet stable.
   o  The Shim6 technical specifications have yet to resolve all known
      design choices.
   o  The extent to which the Shim6 architecture is well-understood has
      yet to be thoroughly gauged.
   o  There is no Management Information Base (MIB) available for Shim6.
   o  There is neither implementation nor operational experience of
      Shim6.
   o  The Shim6 architecture has known technical ommissions.

.  Security Considerations

   Security considerations go here.

.  IANA Considerations

   IANA considerations go here.

.  Acknowledgements

   This work was supported by the US National Science Foundation
   (research grant SCI-0427144) and DNS-OARC.

.  References

10.1  Normative References

   [I-D.ietf-shim6-arch]
              Huston, G., "Architectural Commentary on Site Multi-homing
              using a Level 3 Shim", draft-ietf-shim6-arch-00 (work in
              progress), July 2005.

10.2  Informative References

   [I-D.ietf-multi6-v4-multihoming]
              Abley, J., Black, B., and V. Gill, "IPv4 Multihoming
              Practices and Limitations",



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              draft-ietf-multi6-v4-multihoming-03 (work in progress),
              January 2005.

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC3221]  Huston, G., "Commentary on Inter-Domain Routing in the
              Internet", RFC 3221, December 2001.

   [RFC3582]  Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
              Multihoming Architectures", RFC 3582, August 2003.


Author's Address

   Joe Abley
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City, CA  94063
   US

   Phone: +1 650 423 1317
   Email: jabley@isc.org

Appendix A.  Change History

   This section should be removed prior to publication.

   draft-ietf-shim6-applicability-00:  First draft, largely incomplete,
      submitted to facilitate comments on general structure and
      approach.




















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Acknowledgment

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   Internet Society.




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