Survey of Proposed Use Cases for the IPv6 Flow Label
RFC 6294

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Independent Submission                                             Q. Hu
Request for Comments: 6294                                  B. Carpenter
Category: Informational                                Univ. of Auckland
ISSN: 2070-1721                                                June 2011

          Survey of Proposed Use Cases for the IPv6 Flow Label

Abstract

   The IPv6 protocol includes a flow label in every packet header, but
   this field is not used in practice.  This paper describes the flow
   label standard and discusses the implementation issues that it
   raises.  It then describes various published proposals for using the
   flow label and shows that most of them are inconsistent with the
   standard.  Methods to address this problem are briefly reviewed.  We
   also question whether the standard should be revised.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see 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/rfc6294.

Copyright Notice

   Copyright (c) 2011 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.

Hu & Carpenter                Informational                     [Page 1]
RFC 6294                  Flow Label Use Cases                 June 2011

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  A Brief History of the Flow Label  . . . . . . . . . . . .  2
     1.2.  The Flow Label and Quality of Service  . . . . . . . . . .  3
   2.  Flow Label Definition and Issues . . . . . . . . . . . . . . .  4
     2.1.  Flow Label Properties  . . . . . . . . . . . . . . . . . .  4
     2.2.  Dependency Prohibition . . . . . . . . . . . . . . . . . .  5
     2.3.  Other Issues . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Documented Proposals for the Flow Label  . . . . . . . . . . .  6
     3.1.  Specify the Flow Label as a Pseudo-Random Value  . . . . .  7
       3.1.1.  End-to-End QoS Provisioning  . . . . . . . . . . . . .  7
       3.1.2.  Load-Balancing . . . . . . . . . . . . . . . . . . . .  8
       3.1.3.  Security Nonce . . . . . . . . . . . . . . . . . . . .  8
     3.2.  Specify QoS Parameters in the Flow Label . . . . . . . . .  8
     3.3.  Use Flow Label Hop-by-Hop to Control Switching . . . . . .  9
     3.4.  Diffserv Use of IPv6 Flow Label  . . . . . . . . . . . . . 12
     3.5.  Other Uses . . . . . . . . . . . . . . . . . . . . . . . . 12
   4.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   7.  Informative References . . . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   IPv6 is being introduced to overcome the address shortage of the
   current IPv4 protocol, but it also offers a new feature, i.e., the
   Flow Label field in the IPv6 packet header.  The flow label is not
   encrypted by IPsec and is present in all fragments.  However, it is
   used very little in practice, for reasons discussed below and in
   [Amante11].  After a short introduction, this document summarizes the
   current specification of the IPv6 flow label and some open issues
   about its use in Section 2.  Section 3 describes and analyzes various
   proposals that have been made for its use.  Finally, Section 4
   discusses the implications and attempts to draw conclusions.

   The Flow Label field occupies bits 12 through 31 of the IPv6 packet
   header.  It provides a potential way to mark a packet, identify a
   flow, and look up the corresponding flow state.  This field is always
   present in an IPv6 header, so a phrase such as "a packet with no flow
   label" refers to a packet whose Flow Label field contains 20 zero
   bits, i.e., a flow label whose value is zero.

1.1.  A Brief History of the Flow Label

   The original proposal for a flow label has been attributed to Dave
   Clark [Deering93], who proposed that it should contain a pseudo-
   random value.  A Flow Label field was included in the packet header