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Versions: 00                                                            
6man Working Group                                           S. Krishnan
Internet-Draft                                                J. Halpern
Intended status: Standards Track                                Ericsson
Expires: April 21, 2011                                 October 18, 2010


            Reserving bits in the IPv6 header for future use
              draft-krishnan-6man-header-reserved-bits-00

Abstract

   The IPv6 header does not contain any reserved bits for future
   expansion.  This document sets aside 4 bits from the flow label field
   for future expansion.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 21, 2011.

Copyright Notice

   Copyright (c) 2010 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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions used in this document . . . . . . . . . . . . . . . 3
   3.  New IPv6 header format  . . . . . . . . . . . . . . . . . . . . 3
   4.  Future use of the reserved bits . . . . . . . . . . . . . . . . 4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5








































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1.  Introduction

   The IPv6 header does not contain any reserved bits and all bits in
   the header are currently accounted for.  This means that it is not
   possible to develop any future extension mechanisms that require bits
   in the IPv6 header.  Mechanisms such as ECN were possible in IPv4
   because there were bits available in the IPv4 header. e.g.  Re-ECN is
   a proof of concept mechanism for ConEx that uses an unused bit (Bit
   48) in the IPv4 header.  It cannot be implemented analogously in the
   IPv6 header.  This document proposes reducing the size of the flow
   label field from 20 bits to 16 bits and setting aside 4 bits for
   future use.


2.  Conventions used in this document

   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.  New IPv6 header format

   This document updates Section 3 of [RFC2460] to reduce the length of
   the flow label field from 20 bits to 16 bits, and in the process
   creating a 4 bit reserved field.  All other fields in the IPv6 header
   remain unchanged from [RFC2460].
























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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version| Traffic Class | Resvd |         Flow Label            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Payload Length        |  Next Header  |   Hop Limit   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                         Source Address                        +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                      Destination Address                      +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Resvd                4-bit reserved field.

      Flow Label           16-bit flow label.

      All other fields are same as those defined by [RFC2460]




                   Figure 1: Modified IPv6 header format

   Senders MUST set the bits in the reserved field to zero and receivers
   MUST ignore them.


4.  Future use of the reserved bits

   New mechanisms that require allocation of one or more of the reserved
   bits MUST require Standards Action as specified in [RFC5226].


5.  Acknowledgements

   The authors would like to Pekka Savola, Christian Huitema, and
   Ingemar Johansson for the discussions that led to this document.




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6.  Security Considerations

   This document does not bring up any new security issues.


7.  IANA Considerations

   This document does not require any IANA action.


8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.


Authors' Addresses

   Suresh Krishnan
   Ericsson
   8400 Blvd Decarie
   Town of Mount Royal, Quebec
   Canada

   Email: suresh.krishnan@ericsson.com


   Joel Halpern
   Ericsson

   Email: joel.halpern@ericsson.com













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